Resin is one of the many forms of plastic that chemistry has bestowed upon the world. One of resin's many forms is that of casting resin, where two different liquid parts are mixed and poured into a mold, where it hardens and produces an exact cast replica of whatever was used to make the mold. Cold cast resin produces a significantly lower amount of heat during the reaction than its cousin products, hence its namesake.
Cold cast resin is a two part polymer resin. Depending on the chemical formulation of the polymer, the two parts are mixed in equal or unequal ratios. Once thoroughly mixed, a two part resin undergoes a chemical reaction that causes the polymer resin to react and harden from a liquid to a solid plastic. Once the reaction is complete, the solid resin is in a stable plastic form that behaves and reacts in similar manners to other solid plastics.
The primary use for cold cast resin is in applications where individuals wish to make plastic duplicates of some master model with minimal supplies. After a master model is obtained or made, a mold of the model is made. When the mold is ready, enough cold cast resin is mixed in the proper ratio to completely fill the mold. It is important that mixing is done slowly enough to not create air bubbles, which will lead to defects, but quickly enough to work within the quick cure time of the resin. Once mixed, pour slowly into the mold, making sure again not to form bubbles. Once hardened, aside from any defects caused by bubbles or foreign objects, the resin will take the form of whatever was molded.
Cold cast resin's primary benefit is the minimal amount of heat that is formed as a result of the chemical reaction between the binary agents that make up resin. Many two part resins, when combined, will generate heat as a result of their combined chemical reaction. For adhesive and sealing resins, such heat can typically be ignored. However, for casting purposes, the confined space of a mold combined with the potential heat sensitivity of the molding material make cold cast resins the preferred choice for people who use such molds.
Since cold cast resin is chemically engineered for low heat production, other qualities, such as cure time and cure strength, are typically treated second. When compared to resins of a comparable price, cold cast resins are typically weaker than their hot cast cousins. That being said, cold cast resins have evolved to the point where their characteristics are acceptable for their intended usage.
Variations within cold cast resin include those that take longer to cure, but will have a greater strength when cast (allowing for thinner parts), or conversely those which quickly cure (which is great for mass production) at the cost of strength. Other formulations allow for the addition of colorants to give the final resin a base color, or to allow the final resin to be completely transparent.