As someone with a fair amount of fancy quilting tools on hand, I would say that my design wall is possibly my favorite of them all. I use it to preview fabric swatches, to organize blocks and to keep my latest project from becoming a wrestling arena for my cats.
So, how does a design wall work? Basically, it's a larger version of a children's felt story board. A rigid base is wrapped in a "sticky" material to create a surface that fabric can both stick to and be removed from with ease.
For my design walls, I started with foam insulation, which can be purchased in sheets from Home Depot. I like the foam insulation because, while it's rigid enough to stay flat, it's also lightweight enough to be portable. (So, even if you don't have a dedicated sewing room, you can make a smaller version that can be easily tucked away in a closet or under a bed when not in use.) If you use foam insulation, you'll also be able to pin notes or whatnot to your design wall, just like a big bulletin board!
For my large design wall, I used two big sheets of foam insulation, each about 48" x 96". The pieces I bought had tongue and groove sides, so I was able to slide the two sheets together and tape them in place before I wrapped them in batting (creating one really big wall). Alternately, I could have wrapped the two pieces separately so they could be used side-by-side or tucked behind one another when less space was needed.
If you go to a place like Home Depot, you'll find a wide array of insulation types. I like to stick with pieces that are about an inch thick. I've found that's thick enough for the finished walls to stand on their own, without being too bulky. If you're looking for a more substantial wall, you may want to go with a thicker product.
Of course, if you only have a little bit of space, you can always make a smaller design "wall" like the one I made today. I used a 24" x 48" piece of insulation for my base and Warm and White batting for my wrap. Some people like to use flannel, but I find that low-loft cotton batting like Warm and White is "stickier". It's also readily available in wide sizes, which makes it nice for wrapping larger walls.
Start by cutting a piece of batting about 4" larger on all sides than your piece of insulation (wider if your insulation is more than 1" thick). On a floor or large table, center your insulation on your cut batting. Most insulation comes with a whole bunch of brightly-colored words on one side, so make sure you're laying the plain white side onto your batting!
Starting in the center of one side, pull the batting tightly toward the back, using a staple gun to secure it in place. It can be tricky to staple into foam and you may have to try a couple of times before you get it to work just right. Apply a good amount of pressure, even if that means you're denting the insulation as you staple. Repeat on the opposite side, stretching the batting smoothly
Reinforce the edges of the batting by covering them with tape, as shown above. I used mailing tape here, but duct tape would be a much better and more durable choice, particularly if you plan to move your wall around a lot. Make sure that your tape both covers all of your staples and extends at least an inch beyond the edge of the batting (onto the insulation). Use more than one piece of tape, if necessary.
I hung this little design wall in a very low-tech way by digging a small hole into the back of the insulation and hanging it on a nail. The insulation is very lightweight, and the batting sort of grabs the textured wall, so it's surprisingly stable!
My larger design wall rests on the ground, leaning against the wall of my sewing room. The top is attached to the wall with wide, sticky-backed Velcro.
Please keep in mind that this is just one of many ways to make a design wall. I've found this method to be easy and durable, but you may find that another method or other materials work better for you.