a brand name for a type of very thin polyester (= a kind of plastic), used to wrap and protect things, as insulation, and for of its shiny quality

Windows have been coated with Mylar to make them blast-resistant. 窗户上涂有聚酯薄膜，防止玻璃爆裂。

You can store watercolours by placing them inside Mylar envelopes in a portfolio. 水彩画可以放在大卷宗夹内聚酯薄膜做成的信封里进行储存。