Polymer clay

Polymer clay is a type of hardenable modeling clay based on the polymer polyvinyl chloride (PVC). It typically contains no clay minerals, but like mineral clay a liquid is added to dry particles until it achieves gel-like working properties, and similarly, the part is put into an oven to harden, hence its colloquial designation as clay. Polymer clay is generally used for making arts and craft items, and is also used in commercial applications to make decorative parts. Art made from polymer clay can now be found in major museums.

Bakelite, an early plastic, was popular with designers and was an early form of polymer clay, but the phenol base of uncured Bakelite was flammable and was eventually discontinued. Polymer clays were first formulated as a possible replacement for Bakelite. One of these formulations was brought to the attention of German doll maker Käthe Kruse in 1939. While it was not suitable for use in her factory, Kruse gave some to her daughter Sophie, who was known in the family as "Fifi," who successfully used it as modeling clay. The formulation was later sold to Eberhardt Faber and marketed under the name "FIMO" (FIfi's MOdeling compound).

Polymer clays contain a basis of PVC resin and a liquid plasticizer, making it a plastisol. Polymer clay plastisol is also categorized as a plastigel because of its rheological properties. It is a high yield thixotropic material; when a sufficient force is applied the material yields, flows like a viscous liquid until that force is removed, whereupon it returns to being a solid. This plasticity is what makes it useful as modeling clay as opposed to putty or paste. Plastigels retain their shape even when heat is applied, which is why polymer clay does not melt or droop when oven cured. Various gelling agents are added to give it this property such as aminated bentonite, metallic soaps, or fumed silica.

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