In general, all plastics allow the transmission of microwaves; however, not all plastics work well in the microwave. It is really up to the manufacturer of the particular container in question to approve it for microwave use since other things have to be considered, such as the wall thickness and strength of the container and the maximum temperature plastic can withstand. Contents of containers may exceed the actual plastic containers' temperature resistance leading to damage to the container and potential injury.

Most microwavable plastic food containers are going to be polypropylene. While, in general, polypropylene is considered microwavable, again, you would need to check with the manufacturer before using it in the microwave. LDPE is also considered microwavable, but it does not handle high temperatures and is often only used for the lid material.

Many of our manufacturers do not recommend HDPE for the microwave, and we suggest you avoid it unless the manufacturer has specifically approved it. PET and polycarbonate should not be used for microwaving as they tend to absorb heat. Acrylic and polystyrene are also not recommended.
Caution should be taken when reheating food high in sugar or fat as they can cause damage to microwave-safe containers. See the microwave manufacturer's instructions for information on using microwave-safe containers in your microwave. Always remove the lid or vent containers before heating in the microwave. Plastic containers that are microwave safe are not intended for ovens, stovetops, or other browning elements.

Among commonly used plastics for labware Polymethylpentene and Polysulfone are the most transparent to microwaves. We recommend their use when the chemical and temperature resistance of Polymethylpentene and Polysulfone is compatible with the heated materials. Fluoropolymers can be used when aggressive chemicals such as acids or solvents are heated; proper venting is essential. Closure threads must be completely disengaged before heating bottles or containers in a microwave.