From Dead Pig to New Sweater

How fibers are being made from slaughterhouse waste

Klara Zietlow
8 min readJan 11, 2021
White and red spools of gelatin yarn on toilet paper rolls
The gelatin fibers all wrapped up nicely. You’d have no idea what they started out as! (ETH Zurich)

Slaughterhouses produce more than 10 million tons of waste a year, just in the EU. These byproducts are an abundant source of collagen. Collagen is a valuable protein because it can easily be turned into gelatin. You might have used gelatin to make jello before. I bet that was pretty great, but there’s only so much of that the world can eat.

Philipp Stössel, a PhD student at ETH Zürich, recognized this waste product’s huge potential and used it as his inspiration for a new fiber.

Well, he wasn’t actually the first one. Some Scottish company filed a patent for gelatin fibers way back in 1894. But since we’re not all wearing gelatin socks, you can see how well that went.

Stössel invented a new spinning technique able to produce a stronger, more water-resistant end product.

There are many types of gelatin available, but Stössel used pork gelatin because its often of higher quality than other types.

How to Make It

Making the fibers is actually quite simple. You could even make them at home! (Just leave out the chemicals ;))

1. Potions Class (make the dope)

Combine gelatin, water, and isopropyl alcohol in a sealable container at 50 degrees Celsius. Mix or shake it every now and then. After 30 minutes to an hour the mixture will separate into two distinct layers.

Three tubes with separated spinning dope
The white stuff on the bottom is our gold 💰 (ETH Zurich)

Once that happens, pour off the supernatant (top part) of the mixture, which in our case is the water and alcohol. You’ll be left with the “spinning dope”, a white, spongy blob of gel. Make sure to do this step soon after separation because if you wait too long, the mixture will become homogenous again. If that happens, you won’t be able to spin it!

2. Squirt it out and s t r e t c h

There are two different methods you could use here. On a high level, they’re both just taking the dope and stretching it out really long and skinny. I’ll explain the similarities and differences between them, but first I think it’s time for…

Stretching 101

You might be wondering: How on earth are you supposed to stretch a sticky blob, Klara? Why, I’m glad you asked! You could point the spinning nozzle to the ground and have gravity do the work for you. That’s the easiest way. But you won’t be certain how much stretch factor is being induced.

If you want to get more precise, motorized rollers covered in Teflon can draw out the fibers at exactly the degree you want them to. All it takes is changing their speed.

Okay, that’s nice. Skinny jello. But why would you want to stretch it out in the first place?

By stretching the fiber out, it actually gets stronger. Stretching improves the material’s structure by reducing its size and therefore also number of defects. Think about pulling on a plastic bag. The harder you pull, the harder it is to tear! That’s because stretching aligns the polymer (or in our case protein) chains making them tougher against strain.

The string hanging down with a weight attatched
A gelatin string from 10 filaments at 2x stretch easily holds a 140 g (5 oz) weight (ETH Zurich)

Of course, you can’t stretch the fiber out tooo much. Stössel found that the sweet spot was stretching to around 2x the original length. These fibers performed exceptionally well in stretchiness, elasticity, strength, and toughness.

This is an interesting finding because only few materials possess high strength and toughness at the same time. (Strength=how much force it takes to deform something, Toughness=how much force it takes to crack something)

Dry vs. Wet

Dry-spinning is the most straightforward (especially if you want to do this at home). Put the precipitated protein (white blob) in a syringe, squirt it out, and stretch it using one of the techniques above. Keep stretching it as long as you would like and if it’s still wet by the time you finish, let it air dry.

What’s great about dry-spinning is that it leaves you with a very porous material which allows for better insulation, if that’s your thing.

The fibers’ center with lots of pores
A cross section of the fiber. Look at all those pores LOL (ETH Zurich)

Buuut, if dense fibers are more your thing, give wet spinning a hand! It produces stronger fibers because it makes stretching easier. Instead of squirting the coagulant out into the air, press it onto a pair of Teflon coated rollers moist with ethanol.

Thin gelatin threads on a black ethanol soaked roller
The white threads on a black, wet roller. That’s how thin they are! (ETH Zurich)

The ethanol prevents the strings from sticking to the rollers. It also ensures that the fibers harden quickly once they’ve been stretched and loaded onto the conveyor belt.

A diagram of the spinning process
The wet spinning process. (ETH Zurich)

The spinning machine Stössel developed was able to produce 200 meters (656 ft.) of filament a minute. He then spun the filaments into a 2-ply yarn with a hand spindle.

It took around a thousand tiny filaments to make the yarn for one mitten. That’s because Stössel’s machine can make these fibers really thin. Each one is only 25 micrometers wide, half the size of a human hair.

Cross-linking and Extra Treatments

All sounds great, right? Well, the fibers are great on their own…but there are some drawbacks. Gelatin is super water soluble (like really really) so when the fibers get too wet they swell and dissolve. It’s also not the strongest which is a problem if you’re going to be making clothes with it.

Since making mitten jello every time you try to throw a snowball isn’t exactly ideal, Stössel experimented with a variety of extra treatments to improve the fiber’s qualities.

Here’s where cross-linking was useful. Cross-linking is taking a chemical and using it to bind the protein chains that make up the fibers together. The connections are called “cross-links”. This makes them much stronger and more rigid.

The most effective chemical combination was ethylene glycol diglycidyl ether (aka EGDE) and formaldehyde. Aren’t chemical names a piece of cake?

Epoxides (the most effective being EGDE) were added at 50% of the gelatin’s weight during the initial mixing. (Although, not all of the EGDE stayed inside the fiber. Some just remained in the water/alcohol mixture.)

Once the fibers had been spun, they were put in a low pressure container with formaldehyde gas for 15 hours.

The resulting fibers were stiffer, more compact, and held together better when immersed in water. They swelled much less when submerged and nearly had the water resistance level of a human hair.

The gelatin mitten submerged in a glass of water
Just in case the mitten wearer falls into a pond, Stössel is prepared :) (ETH Zurich)

In an effort to mimic the water repelling properties of wool, Stössel coated the yarns with lanolin. Lanolin is a 100% natural grease produced by sheep. The newly coated fibers were so great they even survived multiple runs in the lab’s washing machine simulator!

🐰 and Possible Applications

In a way, gelatin fibers mimic those of an angora rabbit. Angora rabbit fur is one of the highest quality, most sought after fibers in the textile industry. Most animal fibers, like sheep wool, have little overlapping “scales” which make them matte. Angora rabbit fibers don’t.

Their fibers are smooth, thin, shiny, and filled with a lattice-type medulla. The medulla is a mostly hollow canal running down the center of the fiber which gives the fiber its lightness and porousness.

A fluffy tan angora rabbit
A duster *ahem* angora rabbit. (Animalogic)

Often if an animal fiber is medullated that’s a bad thing. It usually has a diminished value and less end-use potential, but angora rabbit wool actually benefits from it! The porous structure allows for better insulation, just like a double-walled Thermos keeps your soup warm.

Angora rabbit wool production is limited though and expensive (~20 USD per kg.) This makes it not very accessible to your average person. Rabbits are also not treated very nicely, so we’re better off staying away from rabbit factory listings on Craigslist.

Gelatin fibers shine in the light
Silky fibers, minus the bunny (ETH Zurich)

Gelatin fibers provide the same smooth surface and attractive shine as angora rabbit fibers. They’re porous, repurposing a waste product, and easier to make than wrangling a bunch of bunnies. Could they be the replacement we’ve been waiting for?

Maybe, but unlikely. Gelatin fibers are very sustainable to make and have great properties, but the chemicals used for strength and water-proofing are not.

Stössel compared the gelatin mitten he created as a showpiece to a mitten made of merino wool. They had the same insulating ability, but the wool still had superior water toleration.

The identical gelatin mitten next to the merino wool mitten
The shiny gelatin mitten on the left, next to the matte merino wool mitten on the right. (ETH Zurich)

Then there’s the issue of getting people to wear it. Stössel says, “Sure, people will be skeptical, but many clothing items are made from animal protein, such as silk or leather. And a lot of people have no issues wearing leather jackets.”

So I guess we’ll just wait and see! I’m excited to see how the future of biopolymer fibers will play out. Who knows what other wacky stuff will be made into fibers in the near future!

Key Takeaways

  • A PhD student developed a method of producing fibers from gelatin, an abundant slaughterhouse waste product
  • The fibers are simple to make and don’t require much equipment
  • They have many of the same properties as angora rabbit wool
  • Gelatin fibers are naturally insulating because of their porous structure
  • They don’t perform well when wet and chemicals are needed to make them water-resistant

Sources and Further Readings

Before you go, I’m Klara — a 14 y/o student studying all things science and tech at The Knowledge Society 🧠 Everyday, I make it a goal to learn something new and share it with others around me. If you want to grow your knowledge along with me, be sure to follow me here on Medium, connect on LinkedIn, or get in touch with me at! Also subscribe to my newsletter to get monthly updates on what I’ve been up to and cool resources I’ve found!



Klara Zietlow

Passionate about the future of food and the environment. Likes animals too :)