King Envirosleep® Tempo Polyester Duvet Insert | Summer Weight Marriott Bedding New with tags in package The Envirosleep® Tempo Polyester Duvet insert is an environmentally-friendly polyester fiber fill insert that is perfect for those warm summer nights. These inserts feature a super soft microfiber fabric with a 10 inch baffle box design to keep the filling from shifting. Try this duvet insert today, and sleep in cool comfort all night long.