Kevin MP has wood wainscot in his bathroom. It is very nice looking. Maybe he will weigh in here on the topic.

We are planning on putting wainscot in our masterbath.

I will let Kevin MP weigh in on the warping, but you shouldn't have that much moisture in the bathroom to warp wood and if you do than you have other issues. Think of the wood casing around windows or doors, have you ever seen it warp?

I would say if you have a high water exposure area (like near a tub) i would look into a vinyl type molding (they sell it at Home Depot). That is what we plan on doing for the baseboard molding next to our tub in the hall bath when we redo that next. Our tub/shower curtain is not holding the water and I have noticed damage to the baseboard right next to our tub.

DH and I installed wood wainscoting at DD2s house in her master. He bought the thicker, tongue and grooved boards. Hasn't had any warping or expansion problems.

Here is a link that might be useful: DD2s bathroom

Thanks everyone. My bathroom doesn't have moisture issues. I just don't know anyone who has wainscot in their bathroom. I really love the look.

There is a textured wallpaper that looks just like cottage-style bead board wainscotting. You paint it, so decorating choices are endless. Below is a thread from the Smaller Homes Forum where it is discussed. We talked about it a lot over there, and some used it. Do a search there if you want to see more. There is a beadboard ceiling and beadboard kitchen cabinet doors in old threads on the Smaller Homes Forum.

Here is a link that might be useful: Thread about Wainscott Wallpaper

I used pine T&G beadboard in my recent bath remodel. I live in a humid climate, so I painted all the boards with one coat of paint on the T&G before installing in case I experienced any movement. We did see some slight shrinkage this winter, but it is not noticeable because of they way we painted.