trades > fabrication > plastic > polycaprolactone
document updated 4 months ago, on Dec 15, 2023

PCL plastic being pulled out of boiling water

Fabrication techniques for polycaprolactone

Fabrication techniques for polycaprolactone

Polycaprolactone (PCL) is a hand-moldable plastic that softens when placed in hot water. It's sold under brand names such as Polymorph, Friendly Plastic, PlastiMake, InstaMorph, Thermoworx, and ShapeLock.



Heating methods

Cutting tools

Adhering (or not) to other materials

Thermal staking of plastic

PCL plastic will stick to nearly everything when it's hot — except for parchment paper. The importance of using parchment paper when shaping PCL plastic can not be overstated. It's especially useful for pushing the plastic against a flat surface to flatten that side of the plastic, but parchment paper can be wrapped around other shapes too.

(Side note — The vast majority of tapes refuse to adhere to parchment paper. One of the few that does stick is 3M Nexcare "pain-free removal" medical tape, also known as "3M Micropore S Surgical Tape". It's available at your local pharmacy. I believe this is very similar to other silicone medical tape, but I don't have experience with others yet.)

A list of materials that will stick to PCL when hot, but won't stick very well once the plastic has cooled:

If you want PCL to adhere strongly to a dissimilar material, consider using plastic staking. [2]

TODO — Try making my own version of clay sculpting tools by cutting apart silicone kitchen tools into the right shapes. Test this out, hopefully the silicone won't stick to the PCL at all.

TODO — Similar to the above, note that there are some silicone tools pre-made that may be the right size and shape; [1] [2] [3] [4] [4b] [5] (more)

Making sheets

squishing PCL plastic between two glass plates

The quickest way to make sheets, if having a precise thickness doesn't matter as much, is to squish PCL between two plates of glass with your hands. Amazon and kitchen stores sell glass cutting boards. Hot PCL will stick to the glass, so it's good to wrap the glass with parchment paper, and secure the parchment on the back side with silicone medical tape.

To get sheets of a consistent thickness, use a rolling pin or pasta machine. Rolling pin depth guides can help, and there are two kinds — rings that go around each end of the rolling pin and linear guides that go along the sides of the "dough".

Lastly, flat sheets of PCL and similar thermoplastics are available ready from the manufacturer.

Basic shapes

Turning misshapen sheets into rectangular ones can be done by making cuts with a straightedge and utility blade.

Dowel rods can be made like this: Make a rectangular sheet. Now slice off strips that are as wide as they are deep, resulting in strips with a square profile. The square profile can be made round by heating the surface, and pressing down the square corners until they're roughly round-shaped. This can be done quickly by rolling the strips between two flat surfaces. If you don't need a precisely round rod, the easiest thing is to roll it between your hands. This works up to ~1 cm dowels. TODO — figure out how to make thicker dowels.

Making sharp folds is explained on this page.

Small revisions

It is very useful to provide localized heating to a specific area of your part, so that you can make revisions to that area only, leaving the rest of the piece unmodified. This allows you to iteratively refine the shape over several steps.

Having a tub of cold water available speeds up the hot ⇒ cold ⇒ hot cycle enormously.

When you're working on refining thicker structures, those can be pretty tricky to make small revisions to. Here are some approaches you might think of trying:

  1. Hand-hold half of the piece above water. Unfortunately, thicker structures require multiple minutes to soften completely through, and my arm starts to hurt when holding it out for way less than that.
  2. Jury-rig a mechanism to hang half the piece above the water. This does work, but it might be time-consuming to rig up each time.
  3. I recommend creating separate sub-pieces of the structure, each small enough that it's okay to reheat the entire sub-piece. Then use a heat gun to combine all the sub-pieces together.

Mold-making / casting

(TODO — maybe recreate part of this image for use in this section?)

Similar articles — one, two, three, four.

Similar articles


  1. The reason that thick pieces are challenging to fully heat through is because of plastic's low thermal conductivity.
  2. Here's how to view a microwave's standing waves at home. Also, here's a computer visualization of a microwave's standing waves.
  3. This inexpensive thermometer can read down to -50°C (-58°F), and is well-reviewed by HVAC professionals: UEi Test Instruments PDT650.

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† I haven't yet been able to verify this information either via personal experience or via multiple reliable sources. Take with a big grain of salt. TODO — Verify these.