Tips on Thermoplastics

With unlimited uses for props, masks, costumes, jewelry, scenic details, these thermoplastic materials were developed for the medical industry for use in splints and casts. Some have been available for theatrical use since at least the early '80's.

The primary advantages of thermoplastics over conventional scenic molding and sculpting materials are quick drying/set-up times, lack of unpleasant or toxic fumes or dust, and ease of use by unskilled workers (including children). The main disadvantage is relatively high cost. But, there is no waste...scraps can be heated and reused.

Product Characteristics

Protoplast Sheets: Solid and Perforated Plastic

When you want a nice, smooth surface, and a fairly rigid structure, the solid sheets are the best. The perforated sheets stretch better over deep relief. A stronger, more rigid plastic than Fabric-Form, rather rubbery when soft, strong "memory" (tendency to spring back to original shape) while warm. Can stretch up to 10 times its original size. Best suited to low detail applications, structures, etc. Stretched-out 1/16" perforated makes a great semi-stiff veil lace. Also good for masks people need to see or breathe through. Get a lizard-like texture by sticking a stretched perforated sheet to a solid sheet. Once two softened pieces stick together, it is very difficult to pull them apart. Cuts easily with scissors while warm. Use tin snips, or score and break while cool. Needs to be primed before painting unless you use a self priming spray paint. 18" X 24" sheets, 1/16" thick.

Protoplast Pellets

Pellets are better than sheets for free-form molding, and are perfect for building up relief on the other plastics. When melted in water (in a pan used for crafts), the pellets turn very soft and gooey. It can be sculpted into low detail decorations and shapes. Will take detail when cast in molds. It can also be used as a 'glue' to adhere other plastics to each other, and to reinforce edges, etc. Sold by the pound.

Vara-Form white open woven mesh, 2 weights

Cloth net dipped in plastic. Use the net texure to your advantage when doing bark, vines, etc. Can stretch about 10%. When used for masks and other props, fabric can be glued to it, or stuck to it when the plastic is hot. Can make good light weight structures when texture is not a problem. 36" to 48"W, sold by the foot.


These thermoplastics can all be shaped and formed by immersing in hot water (160°-180°) until soft and pliable, then applying to a mold or form. Dry heat (usually in the form of a heatgun or hair dryer) can also be used for the initial forming or later to build up areas or to reshape. The material can also be sculpted freehand without a mold--the possibilities are limited only by your imagination.

These plastics all adhere to themselves and most other materials readily. When forming over or into a mold, it is best to apply a mold release, such as Vaseline Intensive Care Lotion, to make it easier to remove the plastic from the mold.

The working time before the plastics set varies with the product type, and ambient temperature. Expect two to five minutes working time. Setting time is about seven to ten minutes, and can be sped up by sponging the plastic with cold water. Once it is cool, you can drill, sand, or cut it with normal tools, or glue other products to it with Hot Melt glue, or other adhesives.

These plastics can be painted with common scenic paint, though acrylic-based scene paint (Rosco's Off Broadway or SuperSaturated) seems to be the most scratch resistant. The smoother plastics (Protoplast and Polyform) benefit from priming with Rosco's Tough Prime or other primer for plastics.

Step by step:

1. Find/create your mold.

Use a product that will withstand high heat if you will be using a heat gun.

For more information see The Prop Builders Molding and Casting Handbook by Thurston James.

2. Apply a mold release to the mold.

Aluminum foil works well, but can leave its texture on the plastic.

Vaseline works best. Try Silicone spray for very detailed molds.

3. Bring 1" to 2" of water to a simmer in a shallow craft pan.

An electric skillet set at 200° works well. Materials soften at 160°-180°.

4. Cut thermoplastics into sizes to fit the object you are creating and the way you will work.

For instance, if you want to work like paper mache, cut your FabricForm in long strips 1" to 2" wide. If you want a single piece for a smooth surface, cut your solid Protoplast sheet to slightly larger than your mold.

5. Immerse your first few pieces in the water to soften.

Remember: the Protoplast sheets are tough to separate once they have stuck together. You may want to put them in the water one at a time.

Protoplast sheets and pellets turn clear when warm. Fabric-Form and Vara-Form get soft and floppy when warm.

6. Fish a piece out of the water.

Use tongs, chopsticks, etc.

7. Stretch it onto (or into) your mold, working the plastic into the details.

You may have to hold it in place until it begins to cool.

A hot sponge may be useful to press the material into the mold.

8. Continue to build your project.

9. Use a heat gun to soften and rework areas.

Remember: Fabric-Form will need to be reheated with a heat gun so both pieces are hot at the overlap.

Dip pieces back into the water to soften them for reworking.

10. Use softened pellets as additional 'glue', or use your Hot Melt glue gun.

11. Try sticking muslin or other fabrics to your plastic 'base'

12. Let it cool.

Cooling time will vary, but should not take more than a few minutes. Speed up cooling with cold water.

13. Change your mind.

Heat up sections again, add more layers, etc. (You couldn't do this with Celastic!)

14. Remove from mold.

Cut, drill, sand.

Use regular tools as needed to trim, drill holes for fasteners, etc.

15. Texture.

Add any non-thermoplastic textures, goop. Glue on trim, findings, fabrics, etc.

16. Prime.

Rosco'sTough Prime works well.

Fabric-Form usually does not need priming.

17. Paint.

Acrylic based paints (including spray paints) work well.

Try an Off Broadway or SuperSat Test Kit for an economical way to get several colors to work with.

Use Clear Acrylic Gloss for shiny finish. Or Clear Acrylic Matte to protect your paint with a matte finish.

18. Add bronzing powder for sparkle.

Bonus Tip: When using a face as the mold:

Use lotion for a releasing agent to protect facial hair.

Lubriderm and Vaseline Intensive Care work well.

Blot off excess water, test the heat on the inside of your wrist, and apply.

The water is hotter than the plastic, so blotting it helps eliminate discomfort.

Remember: the face (or hand, etc.) isn't rigid like a mold, so it 'gives' when plastic is pressed into place.

Speed setting time with a cloth dipped in ice water.