Choosing Conductive Threads

Choosing a conductive thread or yarn can be a challenge, as it's not always clear what one should be looking for in a conductive filament.

After inspecting a few threads on the market, we came up with a criteria for choosing a "good" thread or yarn.

This image demonstrates how more surface area can be covered with more conductive filaments.

This image demonstrates how more surface area can be covered with more conductive filaments.

1.) ELECTRONIC FUNCTIONALITY - You should aim for the thread that will apply to the most applications possible.  To us, this means the highest conductivity. Even for resistive heating,  you can create a large surface area heating element with a more conductive thread.A less conductive thread restricts the surface you can cover for just about any application.

2.) MATERIALITY - The yarn or thread you choose should be sewable, weave-able or knit-able in an industrial setting. We optimize for manufacturing at Loomia, so if the material cannot be used in a scalable way, it's not a good choice. When it comes to sewing, the thread should have a small diameter - something under .2" (based on the guide below from Superior Threads).  For knitting, choose something that won't damage an industrial machine, like Jameco 92 thread. Some manufacturers won't run course metallic threads through their CNC knitting machines, so ensure that you choose something that is safe for the threading system.

3.) CONNECTION- Ideally, the yarn or thread should should have an outer metallic coating, making it solderable. Of course, there are many ways to make connections, but having a solderable thread opens up how you can connect the thread to components.

 

 

 

 

As a whole, we haven't seen conductive thread or yarn used widely in consumer products. Aside from Sensoria Socks (which have conductive yarn knit in) or Project Jacquard (which uses a cap touch embroidered grid, many products we've seen online still use traditional wiring or use electronics techniques. For example, the image below shows normal wires with an overmolded "winged" component that allows you to sew the wires to a fabric.

 

 

Stretchable Conductive Ink

Smart clothing only works when all the enabling technologies work. Just like zippers, buttons and thread support our passive clothing, new technologies that bridge apparel and electronics can support our active clothing.  At Loomia   (the company where I work and play), we focus on developing technologies and products that can make our clothing smarter. I think great materiality is important to this industry, so stretchable, direct to fabric conductive inks useful in the sense that they support making circuited clothing feel like normal clothing.

Stretchable inks are normally deposited onto TPU . (thermoplastic polyurethane) and then onto a textile. It sounds like a promising solution, but there have been strong arguments made by Rebeccah Pailes-Friedman and IDTEch Ex Researchers that TPU can pose a problem.

"TPU itself is the first choice of encapsulate but not likely to be the last. This is because it is not the most stretchable thus restricting the clothing-like feeling of e-textiles particularly if large areas are covered. Already companies are experimenting with other material systems ..."  iD Tech Ex  (Source)

My teammate, Ezgi Ucar and I decided to play around with some of our ink formulas to see how they would do deposited onto a stretchy textile. The images and video below show visuals of a highly stretchable and conductive ink that we developed that can be deposited directly onto lycra fabric. We have a lot of work to do to get something like this ready for mass production, but experimenting with what's possible is key to crafting good solutions.