Polycaprolactone: Wonderful stuff

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I recently got my hands on some polycaprolactone, and I’m really enjoying playing with it. It is one of the most useful materials I’ve seen in a long time.

This is a summary of a talk I gave at #HackSTB on 21 August.

So, what is it?

Basically, it’s plastic that you can heat up to just over 60 degrees and hand-mould it into any shape you can think of. It sets as a white plastic that’s strong and tough.

If you want to see some more technical detail, go to Wikipedia

Heating it up

Since it also turns transparent when molten, it’s very easy to gauge the temperature. However, keep in mind that the molten plastic looks the same at 70 degrees as it looks at 170, so don’t overheat.

I’ve found 3 ways to heat it up:

  • Just drop it into a cup of boiling water
  • microwave it (carefully)
  • Heat it up with a hair dryer or blowtorch

The easiest and safest is to just put some into a cup of hot water. In granule form, it melts in seconds and can be removed with a spoon, squeezed to remove water and molded.

If possible, use a heat-resistant glass cup. Some of the plastic will stick to the sides of the cup and, since it’s white, it will be almost invisible in a porcelain cup.

When fresh out of the water, it’s very sticky and will stick to plastic, clothes and skin. Since it does not conduct heat very well, it should not burn on contact when at 60-80 degrees. The outer skin cools relatively quickly and becomes non-sticky, while still being moldable.

It gradually cools down, so remains moldable for a few minutes. If you shape it, be prepared to support it in a shape to prevent it sagging. It can take up to 10 minutes to become self-supporting. You can put it in cold water to make it set faster.

If you have some left over after creating something, roll it into a thin stick shape. This is easy to reheat and can be used as a stirring stick for a new batch, since the newly-melted granules will stick to it.

I would not recommend putting it in the microwave, since it can easily overheat and burn you pretty badly.

I’ve found that, once you have it as a blob, a hairdrier works well to heat small parts of the shape and reshape it. It does take a while to heat up a whole clump, though.


PCL can be hand-molded, but really comes into its own when molded around other things or with the help of something to shape it with.

It easily molds around objects and can pick up very fine surface detail. It can easily be used as a negative mold for a silicone object or for more PCL, if lightly oiled to prevent sticking.

PCL really comes into its own when used together with other materials. It sticks readily to other plastics and wood, and acts like hot glue. It will not stick to HDPE (soft milk jugs, plastic cutting boards) or cling-wrap, so you can use cling wrap to protect an object used as a mold.

Since it’s easy to embed objects in it, PCL can be used for brackets by molding around a bolt head, or can be used to hold a nut for a secure link. It also holds a thread reasonably well.

Since it is a tough, flexible plastic, it is perfect for creating ’living hinges’, simply by pressing it to a thin strip at the hinge line with a steel ruler or something similar.

Colouring and composites

It takes colour very well. I’ve tried using powder paint, and it just soaks up the colour. It should also be possible to mix it with other materials to adjust the properties.

Since it’s slightly translucent, it should make a very nice thin cover for LED light indicators or similar. The LED can be embedded in a block, which solves the problem of mounting it, too.

Fixing Plastic

I’ve used the following method to fix broken plastic objects:

  • Heat a rod of PCL with a hairdryer, and smear some of the molten PCL onto the plastic surfaces to be joined. Take your time with this.
  • Reheat the surfaces until the PCL is molten.
  • Press together and hold.
  • When it’s halfway set, scrape/roll the extra PCL off the join.

This results in a join that is very close to the original strength of the plastic part, and uses a minimal amount of PCL. Of course, this only works for parts that will not be heated above about 40 degrees C.

Surface finishing

When hand moulded, the surface is rough and probably full of fingerprints. A hairdryer or flame can get it smooth and shiny. Just don’t overdo it with the flame, as it will discolor if overheated.

I’ve found that manipulating it with the back of a spoon gets you a very nice, smooth chunky look.

It’s really easy to experiment with this, since you can always just reheat and redo.

Buying it

You can buy it in raw granule form, from several places on the web.

A google search for the following brand names should bring up lots of providers:

  • Polymorph
  • Shapelock
  • Friendly Plastic
  • Instamorph

I got mine from a German producer who calls it Plaast.

At the end of the Wikipedia page is a more complete list of providers.

Availability in SA