Reusable silicone stretch lids are 100% food grade, non-toxic and can be used over and over again. They can withstand low and high temperatures, can be used in microwave (please leave a gap on both sides). Oven proof and freeze-proof with temperature range between -40 to 230 Celsius. Set of 4 includes 1 large (7.5x7.5), 2 medium (5.9x5.9), 1 small (3.9x3.9)