Can I use plastic molds in the oven?

A question that I am asked all the time by my customers is whether plastic molds are suitable to use in the oven for polymer clay, or since the molds are food safe, whether they are safe to use for baking purposes. 

Plastic molds made from LDPE plastic have a maximum temperature of 175°C / 347°F. This means that the molds can handle material with a temperature or material that goes up to a temperature of 175°C / 347°F without getting damaged or ruined. 

Unfortunately, even though the mold can withstand these temperatures, you cannot use the molds in the oven. Using the molds in the oven will melt and destroy them. Even if the molds are not destroyed, they will start warping and will get ruined.

The plastic can handle material with a temperature of 175°C / 347°F, but you need to keep an important point in mind - the mold will only be exposed to these temperatures for a short period of time. If the mold is being used for resin for example, the resin will gradually increase in heat whilst curing and will then decrease again. Therefore the mold will not be exposed to a high temperature for a long period of time. The same applies whether the mold is used for wax, soap, of even chocolate. These materials are at their highest temperature when they're being poured into the mold - which is a temperature that the mold can withstand - but as soon as the material is poured into the mold, it will start going down in temperature to cure, exposing the mold to the high temperatures for a small period of time.

For oven use, silicone molds are the safe and best option. Silicone molds are heat resistant up to a temperature of 200°C / 392°F and for short periods up to 250°C / 482°F. Therefore dough/clay can be baked in the mold. If you are using the mold for food purposes, always remember to make sure that the silicone is food safe.