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, and safe for microwave cooking. Glasslock is BPA Free!! The plastic in most food containers have BPA chemicals that when microwaved the food ingest the BPA Chemical---NOT GOOD!! These clear, stain-proof glass containers feature a space saving, nesting design. Durable silicone seal provides airtight and leak-proof storage. It is ideal for serving and storing, and safe for microwave cooking. All-Natural Glass Vessels with Airtight Lids Ideal for Serving & Storing, Safe for Microwave.