"Mark Ohlund" wrote in message
news
The wainscoting will be painted white like the rest of the trim. In the
books I've been reading, they suggest that MDF works well for the
panels, but still use poplar for the rails & stiles. Is there any reason
I can't use MDF for the rails and stiles as well? This would keep
movement to essentially zero.

MDF is murder on router bits. Perhaps that's a reason to use poplar,
assuming you'll use the router for the rails and stiles. The panels can be
cut on the table saw unless you want a fancy ogee profile, but even so you
can start on the saw so you're removing less material with the router.
Personally, though, for a wainscot I'd stick with either a cove or a bevel
profile, both of which you can produce at the TS.... But i digress. I did
my family room and used MDF throughout.