wrote:
Hi all,
I'm looking to build a room divider 6 feet high by 18 inches wide,
using 1 inch by 1 inch wood. The plan is to paint the frame white, and
fill in the frame with wallpaper. Can anyone recommend a good wood
species that will stay true and not warp over time?
Thanks in advance for your help.

Poplar is a standard hardwood to use when you're planning on painting
or covering it. It's the species that's used for a lot of the
upholsted furniture. It's relatively cheap and takes paint well.

When you say 1" square wood, you'll be asking for 5/4 (say five
quarter) stock. That's a hair over 1", but it's as close as it comes
without having something milled.

R