How to Tell If a Plastic Container Is Microwave Safe

Look for a microwave-safe symbol (a microwave icon with wavy lines) or the words “Microwave Safe” on the container bottom; if missing.

You grab last night’s takeout container, pop it in the microwave, and hit start. Halfway through, the plastic softens, warps, or smells odd. That moment raises a question many people gloss over: which containers are actually meant for microwave use?

The answer isn’t complicated once you know what to check. Between the molded recycling code on the bottom, the official microwave-safe symbol, and a few quick guidelines, you can spot a safe container in seconds. This guide walks through each method so you can heat leftovers without second-guessing the plastic.

What the Microwave‑Safe Symbol Looks Like

The most reliable sign is a small icon molded or printed on the bottom of the container. It typically shows a microwave with wavy lines inside. Some containers also carry the words “Microwave Safe” in plain text.

Per the Chemical Safety Facts, the FDA requires all plastic containers intended for food use to undergo stringent testing before they can carry that label. The symbol means the plastic was tested for heat resistance, structural integrity, and chemical leaching under typical microwave conditions.

If the container has this symbol, you can use it with confidence. If it doesn’t, the icon is not the only clue — the recycling code can help too.

Why Recycling Codes Help Identify Safe Plastics

The triangle of arrows with a number in the center — the plastic recycling code — tells you what type of resin the container is made from. Some resins handle heat better than others, which is why the numbers matter for microwave safety.

• Code #5 (polypropylene or PP): Generally considered microwave safe because it is heat‑resistant and BPA‑free. Many reusable food storage containers use #5.
• Code #2 (HDPE): Also considered safe for short heating times. You’ll often see it in milk jugs and some sturdy takeout containers.
• Code #1 (PET): BPA‑free but not designed for heat. Single‑use water bottles and soda bottles are #1; they may warp or leach chemicals in a microwave.
• Code #3 (PVC): Contains phthalates and should not be used around food, especially when heated. Avoid microwaving anything with this code.
• Code #6 (polystyrene): Foam takeout containers and plastic cups. Can warp and may release styrene when hot. Not microwave safe.
• Code #7 (other): A catch‑all category that may include BPA. Many sources advise avoiding #7 for food heating unless it explicitly says “BPA‑free” and shows the microwave symbol.

Codes 1, 2, and 5 are considered BPA‑free. Codes 3, 6, and 7 carry higher risk when heated. Still, even a “safe” code doesn’t guarantee microwave safety — the container must also be labeled as such.

Simple Test for Unmarked Containers

If the container has no symbol and no code you recognize, you can do a quick check. Microwave the empty container for one minute. If it becomes hot, softens, or warps, it is not microwave safe. For a safer alternative, transfer the food to glass or ceramic.

This at‑home test is a practical workaround, but it doesn’t confirm safety on its own. A container that stays cool and rigid might still leach chemicals if it wasn’t tested for food use. The most secure approach is to rely on the official label. Many consumer health sources, including avoid plastic codes 3 6, emphasize that codes 3, 6, and 7 should be kept away from the microwave entirely.

Don’t rely on code alone — always check for the microwave symbol if the container is reusable. The symbol means the product passed the official tests.

How to Handle Containers Without Any Marking

Many takeout containers, yogurt cups, and margarine tubs arrive without a microwave‑safe symbol. The safest route is to assume they aren’t meant for reheating. Here’s a practical process for any unmarked plastic.

1. Look for the symbol or text: Check every side, especially the bottom. If you see the microwave icon or “Microwave Safe,” you’re good.
2. Check the recycling code: If the code is #2 or #5, the plastic is heat‑resistant, but still not guaranteed. A quick one‑minute empty test can help.
3. Fill with water and test: Place the container with an inch of water in the microwave for one minute. If the plastic stays cool to the touch, it isn’t absorbing microwave energy. If it gets hot, skip it.
4. Transfer to glass or ceramic: When in doubt — and when no marking exists — move the food to a glass bowl or ceramic plate. It’s the simplest way to avoid any risk.
5. Consider reuse limits: Even microwave‑safe plastics can degrade over time. Replace containers that are scratched, cloudy, or warped.

Some consumer health sources, such as the Mount Sinai Children’s Environmental Health Center, advise that if no symbol is present, assume the container is not microwave safe. This conservative rule removes guesswork entirely.

Why FDA Testing Matters for Plastic Containers

The FDA doesn’t test every single plastic container on the market. Instead, it sets standards for materials and requires manufacturers to submit data showing their product won’t leach harmful levels of chemicals or deform under normal microwave use. That’s why the “Microwave Safe” label carries regulatory weight.

For example, a takeout container made from #5 polypropylene may be microwave safe if the manufacturer tested it, but many disposable containers aren’t tested at all. The American Osteopathic Association explains the background of FDA testing for microwave safe and notes that the label means the plastic can withstand heat without melting or releasing chemicals into food.

Without that label, you’re gambling with the plastic’s composition. Even containers that survive a one‑minute test may contain additives that migrate when heated for longer periods or with fatty foods.

When you buy new food storage containers, look for the symbol and code #5 or #2. Avoid unmarked takeout tubs for anything beyond a quick reheat.

The Bottom Line

Identifying a microwave‑safe plastic container takes only a few seconds: check the bottom for the microwave symbol, confirm the recycling code is #2 or #5, and skip anything unmarked or coded #3, #6, or #7. When the symbol is missing, transfer the food to glass or ceramic instead of guessing.

If you regularly reheat leftovers in plastic, take a moment to flip over each container and read the markings. Your kitchen routine will be safer for it — and you can trust that your container won’t surprise you mid‑cycle.