Glass is brittle and expands when heated; if the time period between two temperature extremes is too short, the glass can experience thermal shock. And thermal shock is what results in the nightmare of having to clean up glass and lasagna off the kitchen floor. But there is a simple trick that can help prevent this situation and give you some peace of mind — a little liquid. The first and most basic trick is to not bake food in the oven in Pyrex that is lacking moisture. This one simple step will help prevent dangerous thermal shock situations when using your favorite Pyrex baking dish.