Not only can you add a lid to any cup to keep tea hot, but these ingenious lids made from heavy-duty silicone be used in the freezer, fridge, oven, and microwave. Creates an airtight seal on any bowl or cup. Eco-friendly, BPA, and bps-free. Measures 4 inches in diameter. Nonstick, nontoxic, eco-friendly to food and environment. Standing temperature:-40 to 260 degrees celsius. Safe to use in ovens, microwave ovens, dishwashers, and freezers. Hardness according to customized, normally is from 30 to 80 shore. Durable, long-time use.