Plastic is often used in molds for candles that are flat or in two-piece molds. The plastics that are used for this purpose show a good amount of detail and are durable. The main disadvantage of plastic molds is that they develop warps over time; two-piece plastic molds can also be cumbersome to work with. Two-piece molds require special handling if they are to produce attractive candles. The key in preparing two-piece molds is to get the plastic clamped together firmly enough to keep the wax from seeping out.