Food processing plants use polypropylene in sheet form with labyrinth H-seal.
I believe there are gloss, matt & perhaps pinseal finishes. Pinseal is sort of like leathergrain only finer, quite attractive. Colours are natural, white, black (carbon black), some "poster paint" and some pastel shades. Bay Plastics and many others might do something. Polypropylene is popular because it is steam cleanable.
As I redo each of a relative's kitchen cupboards in euro oak I use white gloss polypropylene backing sheets flush to the wall. Makes fixing a bit more interesting (Rigifix M6 or metal kitchen cupboard fixings), but very easy to keep clean. The top I clad in offcuts of polypropylene likewise so extremely easy to clean. The cabinets are Osmo Oak Wax 3164 which works ok.
So it might work for a bathroom, sort of a designer minimalist - without beading every foot or so with "tile panels". If you do tile the bathroom, and it is cold in winter, use Marmox waterproof insulation behind tiles or PIR foam between battens & Aquapanel behind tiles on top. Plasterboard is useless in wet areas, plywood no better, both aquapanel (cement) & marmox (extruded polystyrene not expanded) are totally waterproof.