Studio Contrechoc

design & textile & technology entries

Research: felting conductive threads

Research on different conductive threads, within felted wool.


Checking if and which conductive thread survives felting and can be used making “drawings”  by discoloring of thermochromatic inkt applying current to the thread.


The idea is to insert the threads between the layers of wet felting. Let it dry, measure the resistance, dye the felt in thermo-chromatic ink and check the resistance again. In a former experience the “normal” silver thread was destroyed (broken – not conductive anymore) after this process.


felt from New Zealand 14.70 euro per kg
felting: 6 thin layers: three thin layers – layer of threads – three thin layers
thickness layer of felt: 2.5 mm
wet felting with warm water and soap, 30 minutes
conductive threads: length around 10 inch = 25 centimeters

Room temperature during heating: 20 degrees C. Important because the Thermo chromatic ink has a discoloring point at around 30 degrees C.

Measurements of resistance after felting and drying (checking if the wire is still conductive)

resistance: in Ohm (using a cheap multimeter, 15% of error, most important/relevant in low resistance situation)
1. elinox PSPO 30075: 120 Ohm
2. stainless steel 0.06: 110 Ohm
3. elistat grey Phtgi-STMT 74/3: 1.3 K Ohm
4. elinox orange PSS 30070: 200 Ohm
5. Conductive Thread – 234/34 4ply  14 Ohms per foot (within margin): 17 Ohm
6. Conductive Thread – 117/17 2ply 300 Ohms per foot: 400 Ohm

Measurements of resistance after applying Thermo ink

resistance: in Ohm (using a cheap multimeter)
1. elinox PSPO 30075: 100 Ohm
2. stainless steel 0.06: 84 Ohm
3. elistat grey Phtgi-STMT 74/3: 1.3 K Ohm
4. elinox orange PSS 30070: 300 Ohm
5. Conductive Thread – 234/34 4ply  14 Ohms per foot (within margin): 20 Ohm
6. Conductive Thread – 117/17 2ply 300 Ohms per foot: 600 Ohm

conclusion: the resistance after felting and applying the dye is not really changed for any of the conductive threads.

(In a former not documented comparable test the conductive threads 5 and 6 where not conductive anymore, being broken or corroded. )

Warming (discoloring) effect: (purpose of this setup is investigating the thermo effect)

1. 5V, current 40 mA, effect not visible (because of textile enclosure around metal thread?)
2. 5V, current 50 mA, effect visible after 30 seconds
3. 5V, current 0 mA, no effect (expected: resistance already very high, so a low current)
4. 5V, current 20 mA, thermo effect barely visible
5. 5V, current 180 mA, thermo effect very good and within seconds visible (180 mA is a lot for an Arduino)
6. 5V,  current 10 mA, thermo effect barely visible

Conclusion: to get an effect we need a current of at least 50 mA, fast effect 120-180 mA.
The resistance of the conductive thread in combination with the voltage applied (Arduino 5V, or with a relais a higher voltage).
All the threads have survived this test: the starting resistance is maintainend.
The elinox with the protecting outer layer of textile is isolating the metal thread so the effect is not visible where a bare metal thread with comparable resistance has a visible effect

Of course the length of the thread is linear related to the resistance: with a longer thread you need more voltage to get the same effect.

Current at an interval for maintaining the white line

Our hypothesis is that the high current (180 mA) is not necessary all the time, because the felt is keeping warm along the discolored line even after the current is off. This led to a last experiment:
Can we use a relais and at what kind of interval between current on and off a clearly visible line is maintained?
Using the silver thread number 5:
Heating up time to get a clear white line: 40 seconds (4×10000 milliseconds)
The best maintainence was reached at: 2000 millis UP (Warming) and 500 milliseconds OFF

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Seeing this effect we realized that the thickness of the felt is important. A next experiment will be done using the thread in a sandwich of less (2) layers of felt, and a third using the thread in a combination of 4-5 layers at one side and two at the other side.

Of course also the amount of applied thermo chromatic ink is important. We are thinking about a way of measuring this amount, because at the moemnt we observe that the felt is not absorbing equal amounts everywhere.

Pictures of the first process (felting):

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2.insert conductive threads after 3 layers, and

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3. add three more layers

4. adding hot water and soap

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5. felting by hand power

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5.drying on a steam engine (not using the steam)

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6.checking wires against the light

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7.measuring the resistance: all wires are still conducting current.

————  ————  ————  ————  ————  ————  ————  ————  ————  ————

Applying the thermo chromatic ink: wet

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dried, with current running through thread number 5  (the blue in dried situation is less intense)

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Thermo Ink, bought at Zijdelings , Tilburg, The Netherlands. You can see that the felt is not absorbing the ink evenly.

PS in this e-textile Skill Share workshop:

We experimented with heating circuits.

Very important for the heating circuit is the total resistance of the heating wire (or network, surface). The best total resistance to aim for is 6-10 Ohm, making a current of 500-1000 mA using 5 V. The low resistance wires are used for single lines of heating, the higher resistance wires are used in networks of wires, or heating pad’s, where you want to heat a surface. Depending on the length or the total surface (e.g. conductive fabrics) you choose for the conductive material giving the right total resistance. Then depending on the total resistance you can lower or raise the Voltage used.

Since the generated heat E = V*I (voltage times current), inserting the law of Ohm, you get E = V * V / R.

For a higher resistance you need just a little more Voltage since V is quadratic in this formula.


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