What compounds are used in the manufacture of shower trays? Crocket's friends told me like this: Fiberglass and resin are the most commonly used composite materials for making shower trays. Also, many brands develop and use their own composite materials. The term resin includes rotomolded polymers and polyester resins. The rotomoulded polymer has a nice texture, while the polyester resin has a high-strength, reinforced coating. Resin has a stone-like appearance, but it is not as heavy or expensive.