gbabasd wrote:ad states -> Durably made to withstand repeated bending and extreme temperatures (-4F to 210F degrees).
Keep in mind water boils at 212F at standard atomspheric pressure (1 bar).
which is likely why these are recommended for reheating only.
While that's true, the 212F is just an idealized number, and represents a rolling boil and the upper temperature limit of pure liquid water. Asians who make tea recognize several levels of boiling, starting at about 155F, when bubbles start to form. And slow cookers (crock pots) will steam and bubble on low when the temperature is held at about 180F. In other words, you can cook in these if you use a "low boil."
That said, I agree that you generally shouldn't cook in these. That's because the boiling poinr is usually higher than 212F. If you food has salt, for example, it'll have a higher boiling point (and lower freezing point) So temperatures will exceed 212F by the time it boils, which exceeds the limit of this plastic.
Worse, most foods also have oils, especially those with sauces. They have MUCH higher boiling point, which is why we fry with oil. Before oils boil, it reaches a smoking point (its highest usable temperature before becoming toxic). Extra virgin olive oil smokes at 460F and, avocado and safflower oils exceed 500F. Most oils smoke from 300F-500F. In other words, if you microwave very oily foods for a long time, you can easily exceed 212F, melting the plastic. You can often see the results when reheating greasy foods in styrofoam takeout containers. The container will develop holes where the styrofoam melted. In fact, the holes are often brown as if fried.