Sculpting details in thermoplastic

This page has safety advice that hasn't yet been checked by our safety reviewer. Treat it as general guidance, and follow your game's, venue's or product's own safety rules first.

A beginner-friendly technique for adding raised rivets, filigree, and decorative details to costumes using thermoplastic scraps and pellets.

Thermoplastic scraps and pellets are one of the most versatile detail-making materials in cosplay. When gently warmed, small pieces become soft and workable, letting you roll, press, and shape them into rivets, bolts, rope trim, or decorative panels directly on top of your base piece. Because the material bonds to itself when warm, fresh details stick firmly to a warmed base layer without any extra glue, and the join becomes solid once everything cools. Sheet scraps are usually softened with a heat gun, while pellets are normally softened in hot water; check your product's instructions for which method suits it. Rivets are probably the most popular starting point. Roll a small ball of softened pellets between your fingertips until it is smooth and round, then press it onto a warmed section of your armour. A flat-bottomed tool or the blunt end of a pencil will push it into a neat dome shape. For longer trim like braiding or cord, roll a short sausage and lay it along an edge while both the trim and the base are still warm enough to fuse together. Filigree shapes take a little more practice — working on a silicone mat or a piece of baking parchment lets you build up a flat design first, then transfer it while both pieces are pliable. Sheet offcuts are just as useful as pellets. A thin strip of scrap can become a raised border, a buckle tongue, or a layered scale. Scoring the surface of cooled thermoplastic with a craft knife before reheating helps two pieces grip each other. You can also press textured objects — mesh, lace, a coin, or the eraser end of a pencil — into a soft piece to stamp a pattern before it sets. Safety is important whenever you use a heat gun or handle freshly warmed thermoplastic. Keep the heat gun moving so it does not concentrate in one spot, and check that the material is cool enough to handle with a brief touch before you work it with your fingers, using a tool instead if it is still too hot. Freshly softened thermoplastic retains heat longer than it looks like it will, so set pieces aside on a heat-safe mat rather than holding them continuously. If you soften pellets in water, use hot water from a kettle, lift them out with a spoon rather than your fingers, and never heat them in a microwave. Work in a well-ventilated space, and younger makers should have an adult nearby to supervise the heat tool. Check the packaging for your specific product, as working temperatures vary between brands and formulations. Once your details are cool and secure, light sanding smooths any fingerprints, and a coat of flexible primer helps paint grip the surface evenly. Because thermoplastic is paintable, sealable, and relatively lightweight, detailed pieces built this way hold up well through a busy convention day.