Polyurethane laminate (PUL) is the most common fabric used in cloth diaper covers and the shells of all-in-one, all-in-two, and pocket diapers. Wet bags are also made from PUL.
PUL is commonly made from polyester. A polyester fabric is paired with TPU (thermoplastic polyurethane), a thin stretchy plastic film, and bonded together using a combination of heat, pressure, and adhesive.
This video from Sewing Bee Fabrics does an amazing job of explaining what PUL is, how easy it is to care for, and even shows you what it does when it get’s wet. This is a sewing video, so if you’re not interested in hearing about how it is sewn as well, you’ll just want to watch the first six minutes or so.
PUL can be washed and dried on moderately high-heat settings. It can also be bleached without getting damaged or color faded. As the video explains, the biggest threats to PUL are abrasives; very high heat can also be damaging over time.