PUL is a kind of plastic/rubbery coated fabric suitable for diaper outsides, bibs and changing pads etc. it feels almost like pleather but softer.
Care instructions: machine wash in warm water, hang to dry or tumble dry using medium heat, limit bleach to occasional use to avoid breakdown of PUL fabric, Do not iron! (that is why I wondered how the ironing of Wonderunder went)
However....it does say -After sewing, seal needle holes in PUL fabric by placing in clothes dryer on high heat for 20 minutes.