Can You Microwave It? Materials & Containers

Microwaves heat by exciting water molecules — so what fails in a microwave usually isn’t the heat itself, it’s metal arcing, plastics softening and leaching, or a container with no water in it overheating. Here’s how to tell whether the thing in your hand is microwave-safe, with the common materials and containers below.

How to tell if something is microwave-safe

• Look for the symbol. A microwave-safe mark (usually wavy lines) or “microwave safe” text on the base is the fastest answer.
• No metal. Foil, metal trim, twist ties, and dishes with metallic paint can spark (arc). Keep all metal out.
• Know your plastic. The recycling number matters — polypropylene (#5) is the usual microwave-safe plastic; polystyrene (#6, “Styrofoam”) and many others soften and can leach.
• Never run it empty. Ceramics and glass need food or liquid to absorb the energy; heating an empty or nearly empty vessel can crack it.

Common items in the microwave

Item	Safe?	Why / condition
Aluminum foil	Unsafe	Metal arcs and can spark a fire.
Styrofoam (polystyrene, #6)	Conditional	Only if marked microwave-safe; plain foam can warp, melt, and leach.
Glass (no metal trim)	Safe	Tempered/borosilicate glass handles microwaving well.
Ceramic / stoneware	Safe	Safe unless it has metallic glaze or paint.
Polypropylene container (#5)	Safe	The usual microwave-safe plastic; vent the lid.
Paper plate (plain)	Safe	Fine for short heating; avoid ones with metallic print.

We’re adding a dedicated page for each material, container, and brand — with the exact condition and what happens if you get it wrong. Check back as the database grows, or tell us which item to prioritize.

General guidance — check your label. Answers here are based on manufacturer specs, USDA/FDA guidance, and material science, but individual products vary by line and generation. Always defer to the symbol or care instructions printed on your specific item. When in doubt, don’t heat it.