According to the manufacturer’s guidance, it’s completely safe to reheat and defrost food in these handy plastic pouches.
Most Ziploc bags are made of low-density polyethylene plastic (LDPE). This material is favored because it has a higher melting point than other types of plastic.
Polyethylene plastic used commonly in making bags begins softening around 95 degrees Fahrenheit (93.6 Celsius). Ziploc bags will melt when they are put in boiling water.
When planning to microwave a Ziploc bag or other plastic bags like Glad sandwich bags, it’s important to ensure they’re labeled as microwave-safe.