I saw a post on here recently about covering walls in fabric. Love the idea by the way, but got me wondering... would it work to cover a wall in flannel so it could be a design wall?

I don't think so. From what I read, the fabric needs to be "glued" to the wall like wallpaper is. Flannel that is straight up and down might not hold pieces very well -- especially blocks and strips; usually you want to be able to pin into a design wall just in case. I wouldn't want to try to put pins into a wall.

Also, I can't help thinking how fast flannel would capture dust and pet hair.

i think you could do this if you used the attaching the fabric to a 1x2 that has been attached to top and bottom of wall may also want to add batting for added weight

I have a large piece of flannel thumb tacked to my wall and it works fine. So far I don't have problems with the blocks falling off.

My design wall is a very large piece of flannel taped at the top, bottom, and sides to the wall. (actually, it is two large pieces that are seamed in the middle)

The pieces stay up just fine till I start joining the blocks together. Then I just add a straight pin to them to help them hold.

Not if you mean to 'wall paper' it on. If you just use push pins to hold it to the wall it would work great. That is how I hold my flannel backed table cloth to the wall.....

My design wall is a piece of "flannel" backed vinyl so it's much sturdier than fabric flannel or batting. I used tiny tacks about 10" apart to tack it to the wall. It's pretty thick, so maybe you could pin it without going all the way to the wall - I haven't had to pin because it holds so strong.

I have had a 100% cotton batting stapled on top of Homesote (pressed paperboard-Home Depot/Lowe's) for a design wall for more than 20 years. Pieces of fabric will stay on forEVER w/o any pins as long as it isn't extremely heavy. I have removed the batting and washed it once or twice, but I often use a lint roller to clean it up of threads. Never use a batting with any Poly in it... your fabric will immediately fall on the floor. Good flannel will work as well. My board is framed and screwed into my wall. "Thanks, Honey!"

I took a flannel queen sheet and used push pins to hold it to the wall, worked great for the whole time I had that house.