Liquid resin is a synthetic fluid that, when mixed with a hardening agent, quickly dries into an extremely durable solid. Some of the most common liquid resins are epoxy, polyurethane, silicone, and polyester. Due to their moldable properties and their final hardness, these resins have many applications. They are used, for instance, to produce floor coatings, electronics casings, and even decorative sculptures. One of the most popular applications of liquid resin, however, is casting.

Resin casting is a process in which liquid resin is combined with a curing fluid and then poured into a mold. When the curing agent meets the resin, a chemical reaction results, causing the mixture to heat up and then quickly harden, retaining the shape of the mold into which it has been poured. Once fully hardened, the casting is removed from the mold and, depending on the needs of the caster, may be sanded, painted, or joined to other molded components.

This process is commonly used to produce dental castings, industrial product mockups, and toys. Liquid resin casting supplies are fairly inexpensive and the process can be easily performed in a home workshop. As a result, it is also widely employed by recreational crafters and hobbyists to produce jewelry and scale models of cars, airplanes, and so forth.

The molds used for resin casting are typically made from a flexible rubber and may be produced by the user, purchased from a specialty shop, or specially ordered. These molds can be made to include high levels of fine detail transferred to the casting, thus making resin casting an attractive option for those who wish to produce intricate, accurate pieces. As the chemicals contained in liquid resin combined with the heat produced by it can be destructive, however, casting molds usually begin to break down with extended use. Thus resin casting is not generally suitable for wide-scale production.

Casting supplies and liquid resins are widely available from hardware and craft shops as well as hobbyist websites and catalogs. Once hardened, resins are usually non-hazardous. While in their liquid state, however, they can aggravate the eyes and skin, and their fumes can cause a feeling of illness if inhaled in large quantities. Users should take safety precautions when working with liquid resin. It is advisable to read all product instructions, wear gloves as well as safety goggles, and to avoid working in closed-up, unventilated areas.