The bathroom is the room where the question about wood comes up most often. So here is the answer straight away: a KUUDU of oiled oak works in the bathroom if the bathroom is ventilated and the shelf does not hang where water splashes every day. Both can be checked beforehand. What the materials do and do not do, with the numbers, follows below.
What bathroom air does to wood
Wood adjusts to the air around it. At 20 degrees and 50 percent humidity, oak settles at 9 percent wood moisture, at 70 percent at 13, at 80 percent at 16, at 90 percent at 21. The German consumer advice centres give 40 to 60 percent for living rooms and warn that from 70 to 80 percent directly in front of a wall, mould grows. After a shower a bathroom is briefly above that, which is normal; the question is for how long. The consumer advice centres and the German Environment Agency say the same thing: open the windows wide immediately after showering, five to ten minutes, in winter three to five are enough. A bathroom in which the humidity then drops back to living-room level is a room like any other for wood. An internal bathroom without a window and without ventilation, where it stays, is not, and no wooden shelf belongs there either.
The veneer of a KUUDU board breathes with this climate, but it does not warp: the core of the board is powder-coated aluminium, which takes on no moisture. What changes in humid air is the surface. Oiled wood goes duller after many humid cycles and wants re-oiling sooner than in the living room. The bathroom shelf page says every one to two years; if you shower long every day and ventilate little, you are at the lower end.
Why the aluminium is not the question
Rust needs iron. The posts, caps and board core of a KUUDU are aluminium, and aluminium protects itself: it covers itself with an oxide layer through reaction with the oxygen in the air or with water vapour, which prevents further attack. The industry association Aluminium Deutschland writes that the material can therefore be used in construction without corrosion protection. This natural layer, however, is porous and turns grey over the years; a coated surface is more durable and keeps its colour. That is exactly what the powder coating on the KUUDU parts does. A scratch down to the metal exposes aluminium, which tarnishes matt, and nothing else. The metal is not the question in the bathroom.
Three rules that make the difference
First: outside the splash zone. A shelf next to the washbasin or opposite the shower gets humid air, and that it withstands. A shelf in the shower or right next to the bath gets water every day, and standing water is the one thing oiled oak does not forgive. The line is easy to find: where there are drops on the floor after showering, no wood hangs.
Second: nothing wet on the board. The wet towel belongs on the hook, not folded on the level; the dripping shampoo bottle on a tray or a coaster. And third, less obvious: perfume, nail polish remover and aftershave are solvents. On an oiled board they leave a mark because they dissolve the oil, just like vinegar and spray cleaners when cleaning. That is what the box or a tray is for. Everything else about care is in the care article; in the bathroom all of it applies, only more often.