Which of the following materials is considered microwave safe?

Glass is considered microwave safe because it is made from materials that do not absorb microwave energy, allowing it to heat evenly and safely in the microwave. This property makes glass ideal for cooking and reheating food, as it can withstand the heat generated during the microwave process without breaking down or releasing harmful substances. Additionally, glass containers are often designed for use in microwaves, often marked with safety symbols to indicate that they can be safely used in this appliance.

Metal, on the other hand, can cause sparks and potentially start a fire in a microwave due to its ability to reflect microwaves rather than absorb them. Wood can also be problematic because it can heat up and may even catch fire. Cardboard, while it might not spark, can also catch fire or may not be able to withstand the heat and moisture from food being microwaved. Therefore, glass stands out as the safest option among the choices provided for microwave use.