5 Things to Know Before Buying conductive fabric

Unique Properties

Link to Qicai

Conductive fabric offers the softness and malleability of fabric, while also having electrical properties. It's mainly used in projects where a soft, flexible and sometimes washable circuit is needed. It's also great for creating low profile switches in projects where manufactured and hard conductive materials are not appropriate.

Fabric can be cut, sewn, stretched, crumpled and manipulated in other ways that hard metals, carbon and plastics can not. Knowing how it behaves can lead to unexpected creative applications and end up solving specific design problems. Not all applications need to be wearable. For example, take a look at Adrian Freed's Tablo Fabric Drape Sensing Controller that uses the fabric's ability to stretch and have tension as a tactile musical interface.

One of my favorite projects is the Massage Me Jacket, a video game controller that gives the wearer a massage as the gamer back + front + kicks their way through Street Fighter II. Hard switches would definitely not be suitable for this design!

IM Blanky is a beautiful example of intricate cuts and hand-built soft sensors on a large scale. It has 104 soft tilt sensors and uses traditional embroidery techniques. The creator describes it's function as such: "By draping it over an object the blanket reproduces digitally and in real time that which it covers." Super cool.

Biggest Downfalls

Having listed some of the great things about cond. fabric, it's only fair to list some negatives.

I would say the biggest con is that conductive fabric comes uninsulated, so when building circuits, it's susceptible to noise and interference from outside sources, as well as noise generated by the circuit itself. It also gives a lot of opportunity for short circuits.

Another challenge, which is related, is that cond. fabric erodes over time. To make fabric conductive you coat or impregnate it with metal. Sometimes this metal and fiber bond isn't the strongest, so it wears down and wears off through use. Depending on what metal is used it will also oxidize since it is not properly insulated. There are ways to insulate, this is gone over in the "how to insulate" step.

A good challenge would be to design a project that highlights these negatives, thus turning them into positives to you can work with.

A Bridge Between Demographics

Conductive fabric can be an excellent way to introduce electronics to a wider group of people, such as knitters, weavers, textile artists, fashion designers and a younger age group. It has helped close the gap between fashion and engineering fields, making a new breed of fashion technologists. Designers are finding they want to learn more about programming and electronics and engineers are getting interested in how fabric behaves and best techniques for building with it.

Leah Buechley, the inventor of the LilyPad Arduino, has been a pioneer for teaching girls and women electronics and programming, teaching workshops and writing books that use materials such as conductive fabric. Check out some of her projects and I recommend reading one of her papers on electronics and education.

Like other fabrics found in the store, conductive fabric comes in different weights as a woven, knit or nonwoven textile.

Knitted fabrics provide stretch and can drape beautifully. A woven or non-woven will not have any stretch to it, unless it is woven with an elastic fiber, such as Lycra, but this is not commonly found in conductive fabrics.

Different fabric weights are usually described by how many ounces per square yard it weighs. However, this isn't usually found when shopping for conductive fabric. You can get a sense of weight if the manufacturer lists a fabric as light, medium or heavy weight. However, these terms can mean different weights per square yard depending on whether it's knit, woven or if the manufacturer knows their stuff. Long story short, ask for swatches or minimum cuts so you can feel and see it for yourself.

When deciding on whether to use a woven, knit or nonwoven conductive fabric, think of what material the conductive fabric will be attached to and what it will be used for. How does it need to drape and move? Will it take a beating and need to be able to take abrasions over time?

Below I've listed some pros and cons of the three choices.

Stretch

Knitted fabric that stretches is perfect when you need traces or switches that need to stretch with the substrate it's attached to. There are light to medium weight fabrics that can be readily found. Some are made using yarns that are blended with natural fibers and coated, which make them soft and very elastic.

Others are knit with thin wire, which makes for a chunkier and less stretchy material. These don't spring back at all, but can be formed into sculptural shapes. It all depends on what is needed for your project.

Pros

- Perfect if the conductive fabric is being attached to a knit, or a material that needs to expand and contract.

- Knitted stretch fabric can be cut in thin straight ribbons which can be softly bent around curves, which a woven will not be able to do.

- The resistance to current changes once you stretch the fabric, which means that it can be used as a stretch sensor. However, the value reading will be jumpy and unreliable. It will not be the same solid range with each uniform stretch.

Cons

- The change in resistance as it moves is also a con and can be troublesome. This can mess with sensor readings, preventing proper current to get to your LED, motor, etc. Don't use it if your circuit requires fine tuned current and resistor values. You may still find it useful only as traces that data flows through, or switches and capacitive touch pads.

Woven

There are many choices when it comes to woven conductive fabric. Screen mesh, twills, taffeta and more are available for purchase. Ask for swatches and samples from online resources to see which ones are right for your project.

Pros

- More choices of weight, fiber content and electrical properties available.

- Relatively stable in it's conductivity and electrical properties.

- Resistance is relatively low in many woven conductive textiles, which is good when using them for power and data lines.

Cons

- Does not stretch or conform as well as knit.

Nonwoven

Nonwoven fabric is a material made from fibers that are bonded together by chemical, mechanical, heat or solvent treatment. Most are laminated with a protective coating, which may need to be removed in order to make contact with the fiber. These can be robust and have an industrial feel.

Pros

- Low resistance can be found in non-woven conductive fabric.

- High resistance nonwovens can be found. The thicker, squishier ones make for great force sensing resistors.

- Some are more breathable than tightly woven fabric.

- Bonding methods can add strength, stability and durability not found in wovens and knits.

Cons

- More difficult to find and not readily available in small quantities.

- Can be stiff and thick, which doesn't make them optimal for integration into clothing and other items where you want to maintain a soft drape.

Ohms Per Square

Conductive fabrics are made up of different fibers (e.g. nylon, cotton) and conductive metals (e.g. stainless steel, silver, copper). The resistance of a particular fabric depends on what conductor is used and how it is made. When purchasing conductive fabric the unit of resistance will be listed as Ohm/Sq or Ω /', meaning Ohms per Square. This unit of measurement calculates the sheet resistance of a material.

What does it mean?

If a fabric is labeled as 2 Ω per ' it means that when the material is cut in a square, no matter how large or small that square is, it should be 2 Ohms. If cut in another dimension, such as a rectangle, the Ohms per inch are multiplied by the aspect ratio. For example:

If we define a 1" square an one unit and cut a rectangle that is 1" x 3", the aspect ratio if that rectangle is 3.

2 Ω (per ') x 3 (aspect ratio) = 6 Ohms

The thickness is also taken into account when coming up with this unit. If you wanted to calculate your own sheet resistance, two multimeters and 4 probes would be needed. We won't go over how to do this, the resistance you measure using your one multimeter will be more useful to you and your projects. If you would like to learn more, check out this explanation of Four Point Probe Resistivity Measurements.

Figuring Out Resistance

So, now we know what Ohm/Sq. means. This measurement is different than the resistance you will need when figuring out what voltage and current you will need and so on. It is helpful when buying material, look at this measurement as a guide to get a sense of it's conductivity.

The circuits you build will be made of specific sizes and shapes created by you. To get the resistance, cut you basic shapes and keep a multimeter by to test each trace or shape that you make. You may be able to come up with a unit of measurement yourself. If you are cnc cutting swirls and know that one swirl is 6 Ω, you then know that when you make your larger circuit, comprised of 10 swirls, the resistance will roughly be 60 Ω.

Voltage/Current Ratings

Most fabrics I have found and worked with do not state the current or voltage that the material can handle. If it is not available, be cautious when working and the manufacturer for advisement. Remember that it's uninsulated, so you if you are pumping a good amount of power through an exposed circuit, it can be dangerous. Be extremely careful not to create a short, you could get electrocuted! Jump to the step on insulation to learn how to protect and insulate yourself and the circuit from contact and weather conditions.

Conductive Vs. Resistive

Electrical conductivity measures a material's ability to conduct electrical current. If a material has high conductivity and low resistance, current moves freely through it.

Electrical resistivity is the measurement of how strongly a material opposes the flow of electrical current. If something has high resistance, it therefore has low conductivity.

Fabrics with electrical properties can be put into either category. I can't put a particular cut off point where one material becomes resistive and not conductive, because it will always be conductive and have resistivity. From my experience, when a fabric is called resistive, it usually means that it will measure to be 1K Ω/' or more.

When thinking of what makes a fabric conductive, I remind myself that wire typically used for traces and connections can be anywhere from .02 - 10Ω. This is dependent of length too. Always grab the multimeter to test for yourself!

How to Choose for a Specific Purpose

When used to replace traces in an electrical circuit, the fabric you want to use is the one with the lowest resistance.

For contactswitches, the same is true, choose a fabric that has low resistance. You can get away with high resistive fabrics sometimes, but it's easier to stick to one rule.

Capacitive touchswitches can be made using material that has a fairly high resistance, the change in voltage is all that is being detected.

Resistors can be replaced using resistive materials by cutting the right dimension of a resistive material to equal the value you are looking to replace.

When pressure or force is applied to piezoresistive materials the electrical resistance changes. This makes them ideal for creating sensors, especially force sensing resistors (FSRs), bend sensors and stretch sensors.

There are a few ways that conductive fabric can be cut. Below is a list, with a description stating pros and cons of each.

Scissors and Blades

Some materials will be easier to cut than others, ones can feel very soft and can not be discerned from regular fabric. Others feel stiff and are heavily coated with bonding agents and metal. Scissors may become dull quicker if they are being used to cut conductive fabric frequently. There are some knits, that are created with very thin metal wire. For these, "fabric only" scissors that are owned or that can be found in a sewing studio should probably not be used. The thin wires may create tiny notches in the blades, along with dulling them quickly.

Pros

- most accessible

- quick and more collaborative (everyone can use a pair at once) when prototyping

Cons

- scissors may dull quicker

- slower process than other options

- harder to create and duplicate intricate designs

- thin wires may create tiny notches in the blades

CNC Cutting

There are large CNC cutters found in labs and some that can be bought for the home. A favorite of mine is the Silhouette Cameo, which is a table top CNC cutter that can cut fabric up to 12 inches wide and 10 feet long. Silhouette has software that can trace an image, e.g. one created in Illustrator or Photoshop, then cut it. Check out my CNC Conductive Fabric Circuit 'ible for more details.

There are large flatbed CNC cutters can be found in some prototyping and production labs, they are an expensive piece of machinery that is usually contained in the garment business. If you have access to one, you are lucky! They can cut up to 60 inch wide fabric and whole rolls containing yards of fabric.

In larger and collaborative labs, what can be more commonly found are vinyl cutters and printer/cutter combinations. I do not have personal experience with these, but you can purchase canvas and fabric materials to cut on some these machines, so they can probably be loaded with custom material with the proper load settings and perhaps additional backing.

Pros

- can make intricate and measurement specific designs

- one design can be reproduced quickly

- cuts materials that laser cutters can not, such as iron-on fabric

- no scorch marks! Which a laser cutter will produce

Cons

- not as accessible and can be expensive, the table top ones are worth the investment if you do a lot of soft circuits!

Laser Cutting

This method comes with a safety warning. Only cut material that is approved by the laser cutter's manufacturer and read the Safety Data Sheet (SDS) of whatever material is in question. Some materials can release poisonous gases and can combust when hit with a laser. Reflective materials can also damage the lens of the laser cutter, which conductive fabric contains. Find out the fiber content (e.g. nylon, polyester, etc.) and the percentage of metal and which ones are present in the fabric you want to laser, the SDS should contain this. If no one has tested it before on the laser you are about to use, the laser's manufacturer and ask if it will be appropriate.

Pros

- can make intricate and measurement specific designs

- one design can be reproduced quickly

- if the fabric contains a little polyester or another synthetic fiber that melts, the edges will melt slightly as it's being cut and will not fray when handled

Cons

- heat can produce scorch marks on the fabric, use a mask when possible to prevent from happening

- hot-melt (iron-on) adhesives can produce toxic gases and get messy under the heat of the laser, so iron-on fabrics are not doable

These connections are traces to components and components to components. Typically solder is the means of making these connections in a circuit. Some conductive fabric is solderable, but it makes for a weak connection.

There are other options, some are more permanent than others. Whichever option you choose, the most important thing is to make a strong and secure connection. Connections can become breaking points in a circuit, where a lot of strain can occur. We already went through some methods of attachment, but since some of the materials used in those steps are not electrically conductive, they won't be much good when making electrical connections.

There are many ways to creatively make electrical connections. For example, take a stroll down the notion aisle of the local fabric store and see how many metal connectors there are. Magnets, hook and eyes, rivets, metallic trims and much more can be found. Hardware and electronic stores are also excellent places to peruse and dig through for connection solutions. Take your multimeter, this will let you know when you have found something conductive.

The methods that follow I find to be the most common and accessible. After making them, alway test your connections with a multimeter!

Conductive Thread

Use conductive thread to connect perforated boards, fabric and other materials to conductive fabric. Sew small and tight stitches to produce a secure joint that won't rattle around and cause disconnects. Make at least three stitches through both materials for a connection that will last. A sewing machine will quicken the pace but can be finicky depending on what thread you using. When making many small connections, a machine is not always easy to get in where you need to.

Pros

- Flexible and strong

- Can get into small and tight spaces

- Hand sewing is versatile, you have a lot of control

- Sewing machine is quick

Cons

- Hand sewing can be time consuming

Iron-on
This connection can be made using the iron-on conductive fabric, ShieldIt. Overlap two trace ends and apply an iron, melting the bottom trace to the fabric substrate and the top trace to the bottom. The hot melt adhesive itself isn't conductive, so get it hot enough until it becomes liquid like, this way the conductive fabric can make contact through it.

Pros

- Quick and strong

Cons

- Not always suitable for irregularly sized connections

Conductive Z-axis Tape

This stuff works like magic. It's a double-sided pressure sensitive tape that makes electrical connections through the z-axis. Say you have a row of traces that all are individual signals, and you need to connect them to another row of traces. Lay this tape down across all the traces, put the traces you are connecting on top and simply press down matching them up. No shorts will be created, it will only be electrically joined from one traces to it's mate, down through the z-axis. 3M makes the tape I am familiar with, but you can also buy it in smaller quantities at DIY electronic shops. If you want a full roll, call up 3M. I've had good experiences with their sales reps and have been able to get single rolls (samples) or multiple.

Sparkfun

Contact us to discuss your requirements of car upholstery fabric. Our experienced sales team can help you identify the options that best suit your needs.

3M webpage

Pros

- Makes multiple connections at once

Cons

- Not a permanent connection on fabric. It's made to use on polymers and resins.

Snaps

Metal snaps can be sewn or hammered on to create connections that are strong and add modularity to a design. They can be found in many diameters. They can also be used as switches!

Pros

- Solid and strong connections

- They make everything modular

Cons

- They can't be used everywhere because of added bulk

Conductive Glue/Paint

A variety of conductive glues and paints can be bought, such as "wire glue" that contains a silver or carbon compound. You can also make your own by following Instructables and other online tutorials showing you how, usually by using graphite. These mediums open the door to creativity, you can paint, stencil and screen print with some. For connections though, they can be unreliable depending on what they are made of.

Graphite and other micro carbon mediums are relatively high in resistance, which can pose problems in a circuit. You want connections to have little to no resistance such as solder or copper wire. Because of how fun and expressive they are, these mediums are still excellent for teaching simple circuit workshops.

Wire glue that contains silver works well, silver has very low resistance. However it can crack and break over time because it is not made to be used on flexible materials. It's also relatively expensive and comes in small quantities due to it's high level of silver content. This glue is great to have around for repairs.

Pros

- Fun to use in workshop environments

Cons

- Can easily crack, not flexible

- If carbon based, a lot may be needed to make a connection

Conductive fabric is like uninsulated wire. The exposed fabric is susceptible to noise and interference from outside sources, as well as noise generated by the circuit itself. The metallic coating will also oxidize over time, some worse than others, depending on the kind of metal. When it comes to fabric, copper and silver coats oxidize the easiest. Stainless steel has the ability to resist stains and rust, which makes it less likely to oxidize quickly.

Insulating your designs also protects your circuit from short circuits.

There are lots of ways to cover and insulate fabric circuits that are fun and creative. The ones listed below are some of the most common and accessible. All will preserve the decorative and flexible aspect of fabric to some degree.

Embroidery

Done by hand or or with a machine, thread can be whipped around conductive fabric to insulate and create a decorative element. Embroidery is an age-old tradition, there are many beautiful hand stitches that can be coupled with new technology.

Pros

- Keeps the look and feel of a textile

Cons

- Insulates on a small level, best for thin lines. If you hand embroider larger pieces, the threads can move and create openings.

Fabric Paint

There are many fabric paints out there to cover up conductive fabric with. Puffy paints, screen printing, spray paint (for fabric!) and just plain acrylic that can be brushed on. Water based paints air cure, where something like Plastisol for screen printing needs heat to cure. Make sure the paint is thick enough to completely coat the areas.

Pros

- Lots of options

- Versatile

Cons

- Can produce uneven appearance

- Long dry time

- Can be stiff

Interfacing

Interfacing is typically used to add structure and strength to fabric and clothing. It comes as sew-in or iron-on, that is also called fusible interfacing, or fusible for short. It comes in different weights, light to heavy, depending on the effect your want and what weight the fabric is that you are attaching it to. It also comes in woven, nonwoven and knit varieties.

Pros

- Quick and easy to use

- Provides a good and even coverage

Cons

- It's usually something that is meant not to be seen.

Plasti-Dip or other Polymers

Plasti-Dip is an air curable rubber that you can paint on to fabrics. It's typically used for dipping the handles of tools in to get a better grip. Use in a well ventilated area, it expels fumes that can be harmful. It comes in many colors and I personally love the matte rubber look it has.

Pros

- Good coverage

- Can add nice aesthetic to project

Cons

- Hard to get even coverage

Fabric

Fabric itself can be sewn or ironed on top of conductive fabric. Use patches of the same color or create an appliqué look by using contrasting ones.

Pros

- The approach that is the least noticeable

- Maintains a textile hand and look

Cons

- Not any I can think of, it's a good solution :)

Traces are the paths that connect one electric component to another, allowing electricity to flow around the circuit. Usually they are screen printed or etched from copper. When prototyping, they are typically wire or created by using a breadboard.

Fabrics can be cut into thin strips and traversing patterns and ironed on to fabric. Some examples of how to use conductive fabric as traces:

Stretch

- Use to create soft curves on woven or knit

- Iron on with light adhesive or zigzag on when you need the traces to stretch

Woven

- Cut in traversing pattern to stretch with knits

- Cut multiple thin strips to create more complex circuits

Adding Components

When using fabric, curl up the leads on through-hole component to use to sew it down with. Some fabrics are solderable, but the heat from the solder can greatly damage and weaken the connection, so I recommend adding strain relief. Check out the connections step.

Crossing Paths

When building a circuit and designing where the traces should go, you will find that some will need to cross others to get to where they need to go. So the paths don't touch and create a short circuit, use a piece of fabric in between each trace to act as a bridge over the trace that is being crossed.

Data or Power?

It's difficult to find voltage and current ratings for conductive fabrics. Be careful pumping anything more than a few hundred milliamps and 5 volts through. This makes fabric better for data lines rather than running power through.

Conductive fabric is used to make sensors in combination with piezoresistive fabrics, plastic (Velostat) and resistive paint.

How Does it Work?

When an electric current runs through the resistive material while it's stretched or pushed on, the resistance to the current changes. You can measure this change in value as it's being manipulated, essentially making a force or stretch sensor.

Alternatively, you can design a variable resistor, which is what a potentiometer is. A resistor ladder is an easy way to get multiple values. That's what this step goes over how to make, a resistor ladder with 14 different points to press on that will give you a different Ohm reading. Just like a potentiometer, this can be used with a microcontroller or in a circuit that usually calls for one.

Make It!

Materials

• Iron-on conductive fabric
• Velostat or Bare Conductive paint
• Netting, such as tulle
• Fabric (preferably something thick)
• 2 Alligator leads
• Multimeter

- Download the attached pattern and cut out your materials.

- Iron the long conductive fabric contact to a swatch of fabric.

- Iron on the small contact 1/8" from the long one.

Using Bare Conductive paint a solid line over the contact and parallel to the long one, like in the picture.

Using a cut strip of Velostat, carefully glue or sew around the edge. Do not let the glue block where the Velostat meets the contact, they need to be able to touch each other.

- Iron the ladder trace to a thin piece of fabric.

- Lay the piece of tulle over the cond. and resistive strip.

You now have all the components, put it together and test.

- Put the top on so the rungs of the ladder reach over to the conductive fabric trace.

- Clip one alligator lead to the contact of the resistive strip and one to the thin trace. Connect them to the leads of the multimeter and turn to the Ohm setting.

- Press along the length of the top strip, connecting the resistive strip to the cond. fabric, and watch the values go up and down respectively.

The values will not be as smooth or reliable as manufactured hard components. This can be helped in software when using a microcontroller. For example, in the Arduino IDE there is a smoothing example sketch by Tom Igoe that stores a number a values in an array and averages them.

To build more sensors check out Plusea's Bend Sensor and Conductive Thread Pressure Sensor

Capacitive sensing is a way to detect human touch without any or little force.

Almost anything that conducts electricity (cond. fabric!) can work as a touch plate. There are different ways to use capactivive sensing in projects. Below are some examples of how to use it in your next project.

Arduino + CapSense Library

When hooked up to an Arduino using the CapSense library, the capacitance of the human body is sensed by helping the plate to reach a charge when touched. Two pins are used, a send and receive pin, the Arduino tracks how long it takes for the receive pin to change to another state, thus detecting the capacitance. For more detail on how this particular setup works, check out the CapSense library page on Arduino.cc.

Breakout Boards

Many breakout boards are available to use in your capacitive touch projects. One is Sparkfun'sMPR121 breakout, that comes with a hookup guide. Adafruit has several capacitive touch breakouts, some have an Arduino library and require a microcontroller and some you just power up. They also offer up lots of documentation on how to use their boards.

Capacitive sensing is also known as what makes your tablet and a touch screen. To read more about how that works check out this article on MIT's website.

CapSense with Arduino from lara grant on Vimeo.

In this circuit you use conductive fabric to create capacitive switches. The attached code is written by Tyler Crumpton and Nicholas Jones, slightly modified to work with less keys.

Make It!

Materials

• Iron on conductive fabric
• Fabric
• Breadboard
• Hookup wire
• Pronged snaps and attachment tool
• [5] 100 K - 50 megohm
• [1] 8 ohm speaker

Tools

• Soldering iron
• Wire strippers and cutters
• Scissors

- Cut out 5 shapes from conductive fabric

- All the switches connect to pin 2 through a resistor. Jump pin 2 over to a row on your breadboard and connect that row to another so you have 5 openings available.

- Connect pins 3 - 7 to pin 2 via a high value resistor.

- Plug the speaker into pin 9 and ground.

- Create a 5 wire ribbon cable with male headers on one end and male snaps on the other. To connect the wire to the snaps, strip about 3/4" from the end. Cut a small piece of fabric and push the prong through that, then take the wire and wrap it around one of the prongs. Set the male part on top and hammer down, trapping the wire in between.

- Iron the switches to a piece of fabric and hammer the female snaps to the top of each one.

- Snap the cable to each switch and plug the headers in the breadboard connecting to each pin of the Arduino.

- Plug the Arduino to your computer and upload the sketch.

When each key is pressed, a tone will sound for one second.

Exploring the realm of conductive fabric can be an exhilarating journey. It's particularly suited for wearables, soft circuitry, e-textiles, and various other projects that leverage its unique properties. Grasping the fundamental techniques will empower you to make informed design and material choices tailored to your specific applications.

This comprehensive guide is packed with years of experience and preferred resources for further exploration. You will discover techniques such as cutting and attaching conductive fabric, as well as constructing various projects, including:

- A momentary switch
- A linear touch sensor using resistive material
- A basic LED circuit with a switch
- A capacitive touch piano using Arduino and CapSense

Consider this guide a valuable reference to bookmark, favorite, or download for future use. It's designed for low-voltage DC projects to ensure safety from electrical shocks. Feel free to contribute your insights and questions in the comments below!