contiboard

I've never worked with this stuff, and know nowt about it.

Would a bathroom environment be too humid for a cabinet made of this?

(Having to make my own, after trawling and failing to find one to fit the requirements.)

Priscus conti -board will swell if any water or humidity gets onto it,Any open ends have to be sealed or you will have trouble

You can use moisture resistant chipboard to V313 spec. It’s coloured with a green dye. If you go to a new housing development the builders will probably give you some flooring offcuts. The better quality ones will use 22mm thickness and the lesser ones 18mm.
Easier to paint is moisture resistant or exterior grade mdf but not as easy to get hold off for the amount you require.

Thanks Peter, that is what I figured.

And thanks gaffer, yes, I have some of that stuff (flooring grade chipboard). I will probably opt to construct from wood. Only considered the contiboard as it eliminates the finishing tasks, which will take longer than the construction.

I made a bathroom cabinet some 20 years or so ago from Conti -board & it is still going strong in my daughters bathroom, If you give it a good coat of varnish or paint then it should be OK,

When the council did the bathroom refurbs, i made a corner cupboard out of moisture resistant 18mdf, i bought a white gloss slab door from Band Q and made the cupboard to suit the door size. ideal for toilet rolls etc.