The edges of glass lids are protected by a metal ring, so they won't burst even if they are subjected to a lot of impact, and even less so on the sides of the pot.

Glass lids are safe because they do not release chemicals when heated. And transparent appearance can not open the lid directly observe the changes in the internal ingredients, easy to grasp the degree of cooking, glass is a poor thermal conductor, local heat, the heat can not quickly and evenly spread to the whole piece of glass, thus forming a large difference in the temperature of each place, the glass is not heated by the uneven expansion and contraction of the heat, resulting in internal tensile stress.