system
Given the following post, respond as if you're commenting on Reddit:
human
What makes some materials oven-safe but not microwave-safe or vice versa?
gpt
The dielectric properties of the material.  

In oven safe, the material has to take external heating, which will be a function of its heat transfer capacity ie if you heat it too fast, one area will expand too quickly, stressing the material and causing the break.  

For microwave safe, the dielectric properties describe how well the material absorbs the energy, or how microwave transparent it is.  Ideally, you'd want a microwave transparent material so that only the food (particularly the water) absorbs the energy therefore heating/cooking the food.  If the bowl has a high dielectric constant, then the bowl will heat, causing the bowl to crack or be at a temperature much higher than the food being cooked.