Can you microwave plastic bags?

Bags designed for microwave steaming are made of a film tested for the temperature and usually have a vent built into the seam. Ordinary zip-top storage bags are polyethylene designed for cold storage; they soften near boiling and have not been tested for hot food contact. Grocery carrier bags and bin liners are never suitable. A sealed bag of any kind builds pressure, which is why every microwave steam bag tells you to leave a corner open or to stand it upright with the vent clear.

How to do it properly

1. Use bags explicitly sold for microwave steaming
2. Leave the vent or one corner of the seal open
3. Stand the bag on a plate so a leak does not reach the cavity floor
4. Open it away from your face — the steam inside is at 100 °C

What goes wrong

• A sealed bag inflates and bursts
• Cold-storage films soften against hot fatty food
• Printed or coloured bags are not food-contact rated at heat

Other options

• Steam vegetables in a covered bowl with a splash of water
• Use a vented microwave steamer, which is reusable

Other "can you microwave" questions

• Can you microwave styrofoam? It depends — Only if the container is labeled microwave-safe, and most takeout foam is not.
• Can you microwave aluminum foil? No — No — foil reflects microwaves and the edges arc, which can start a fire.
• Can you microwave plastic containers? It depends — Only ones labeled microwave-safe — cold-storage tubs are not among them.
• Can you microwave eggs? It depends — Beaten or pricked eggs, yes. A whole egg in its shell will explode.
• Can you microwave Tupperware? It depends — Yes, if that specific piece carries the microwave-safe symbol on its base.
• Can you microwave paper plates? It depends — Plain white paper plates are fine; anything with metallic trim or a foam layer is not.
• Can you microwave metal? No — No — metal reflects microwaves, arcs at edges, and can damage the oven or start a fire.
• Can you microwave breast milk? No — No — microwaves create hot spots that scald a baby even when the bottle feels cool.
• Can you microwave takeout containers? It depends — Only if the container is marked microwave-safe — most are not, and metal-handled ones never are.
• Can you microwave cardboard? It depends — Plain dry cardboard is usually fine briefly; anything with glue, staples, wax or foil is not.
• Can you microwave glass? It depends — Yes for ordinary heatproof glass; no for leaded crystal, and never straight from the freezer.
• Can you microwave water? It depends — Yes, but very clean water can superheat and erupt when you move the cup.