Spider silk conducts heat as well as metals, study finds

March 5, 2012, Iowa State University
This is one of the golden silk orbweavers spinning webs for Xinwei Wang's research project. Credit: Photo courtesy of the Xinwei Wang research group

Xinwei Wang had a hunch that spider webs were worth a much closer look.

So he ordered eight – Nephila clavipes, golden silk orbweavers – and put them to work eating crickets and spinning webs in the cages he set up in an Iowa State University greenhouse.

Wang, an associate professor of mechanical engineering at Iowa State, studies , the ability of materials to conduct . He's been looking for organic materials that can effectively transfer heat. It's something diamonds, copper and aluminum are very good at; most materials from living things aren't very good at all.

But has some interesting properties: it's very strong, very stretchy, only 4 microns thick (human hair is about 60 microns) and, according to some speculation, could be a good conductor of heat. But nobody had actually tested spider silk for its thermal conductivity.

And so Wang, with partial support from the Army Research Office and the National Science Foundation, decided to try some lab experiments. Xiaopeng Huang, a post-doctoral research associate in mechanical engineering; and Guoqing Liu, a doctoral student in mechanical engineering, helped with the project.

"I think we tried the right material," Wang said of the results.

Xinwei Wang, Guoqing Liu and Xiaopeng Huang, left to right, show the instruments they used to study the thermal conductivity of spider silk. Credit: Photo by Bob Elbert/Iowa State University

What Wang and his research team found was that spider silks – particularly the draglines that anchor webs in place – conduct heat better than most materials, including very good conductors such as silicon, aluminum and pure iron. Spider silk also conducts heat 1,000 times better than woven silkworm silk and 800 times better than other organic tissues.

A paper about the discovery – "New Secrets of Spider Silk: Exceptionally High Thermal Conductivity and its Abnormal Change under Stretching" – has just been published online by the journal Advanced Materials.

"Our discoveries will revolutionize the conventional thought on the low thermal conductivity of biological materials," Wang wrote in the paper.

The paper reports that using laboratory techniques developed by Wang – "this takes time and patience" – spider silk conducts heat at the rate of 416 watts per meter Kelvin. Copper measures 401. And skin tissues measure .6.

"This is very surprising because spider silk is organic material," Wang said. "For organic material, this is the highest ever. There are only a few materials higher – silver and diamond."

Even more surprising, he said, is when spider silk is stretched, thermal conductivity also goes up. Wang said stretching spider silk to its 20 percent limit also increases conductivity by 20 percent. Most materials lose thermal conductivity when they're stretched.

That discovery "opens a door for soft to be another option for thermal conductivity tuning," Wang wrote in the paper.

And that could lead to spider silk helping to create flexible, heat-dissipating parts for electronics, better clothes for hot weather, bandages that don't trap heat and many other everyday applications.

What is it about spider silk that gives it these unusual heat-carrying properties?

Wang said it's all about the defect-free molecular structure of spider silk, including proteins that contain nanocrystals and the spring-shaped structures connecting the proteins. He said more research needs to be done to fully understand spider silk's heat-conducting abilities.

Wang is also wondering if spider silk can be modified in ways that enhance its thermal conductivity. He said the researchers' preliminary results are very promising.

And then Wang marveled at what he's learning about spider webs, everything from spider care to web unraveling techniques to the different silks within a single web. All that has one colleague calling him Iowa State's Spiderman.

"I've been doing thermal transport for many years," Wang said. "This is the most exciting thing, what I'm doing right now."

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4 / 5 (2) Mar 05, 2012
Spider silk conducts heat at the rate of 416 watts per meter Kelvin. Copper measures 401

That's an amazing result. This research could have profound impact on materials science if they figure out how to engineer this deliberately. This is a "Big Deal" experiment.
5 / 5 (1) Mar 05, 2012
I'm wondering what advantage thermally conductive spider silk might be to the spider? I could see how vibration conductivity, maybe electrical conductivity, would benefit a spider. This makes the web a big sensor for the spider, extending her senses beyond her own body.
1.5 / 5 (6) Mar 05, 2012
Am I the only one thinking about the possibility of lighter spacesuits and Firefighting gear? Build the layer that touches the skin with this material and then control that layer directly to maintain optimum temperature.
5 / 5 (3) Mar 05, 2012
As an emeritus fireman, I am wondering why conductivity would be beneficial given that high insulation, moisture control through vapor barriers, and reflectivity at times is what is sought after. It seems that any added material added would be most useful if it simply added insulation against high heat. If it could be used somehow to aide internally cooling, then that would be useful. I would think the same would be true in space suits.
1 / 5 (2) Mar 05, 2012
It's a bit suspicious result for me: people made large pieces of clothes from spider silk - how is it possible, nobody recognized it already?

1 / 5 (1) Mar 05, 2012
i didnt know silver was organic. organic means carbon, right? but isnt silver just silver? an element of its own?
5 / 5 (2) Mar 05, 2012
Combine these abilities with a company (Kraig Biocraft Laboratories, Inc. (KBLB)) that is on the verge of getting genetically modified silk-worms to spin spider silk, and you might see a lot more spider silk in a LOT of products here in the near future.
5 / 5 (1) Mar 06, 2012
Tiburon, I am not sure just getting silk worms to produce spider silk will be enough, there are probably a lot of subtle details in the production process that you don't automatically copy by moving a bloc of DNA from one species to another...but it would be terrific if it works on the first try.
1.4 / 5 (9) Mar 06, 2012
Kraig Biocraft Laboratories, Inc. (KBLB)) that is on the verge of getting genetically modified silk-worms to spin spider silk

Wait, what? I thought they'd already achieved this.


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