Glasslock is made of tempered glass, guaranteeing excellent hardness & durability comparing with general glass and has an absolute airtight function keeping the liquid, moisture & smell inside. Specially there is no trace of harmful environmental hormone to human body in using microwave oven. These clear, stainproof glass containers feature a space saving design. Durable silicone seal provides airtight and leakproof storage. It is ideal for serving and storing. Glasslock is BPA Free!! The plastic in most food containers have BPA chemicals ---NOT GOOD!! These clear, stain-proof glass containers feature a space saving design. Durable silicone seal provides airtight and leak-proof storage. It is ideal for serving and storing. All-Natural Glass Vessels with Airtight Lids.