Jan, I guess you have the idea by now but I googled it.
Description: PUL is a polyester/polyurethane laminated knit fabric with a laminate thickness of 1.33mm. This fabric is waterproof, durable and has a slight crossgrain stretch. This product can be used in making diapers, changing mattress covers and applications that require waterproof fabric.
You have probably seen it. Its what the raincoats are made of.