Here is my indoor target butt it is 6’ x 4’ x 16”. The material is Celotex but some lumber yards call it brown board. When I purchased the material (in 2007) it was $5.50 per 4’ x 8’ x .5” sheet. I had difficulty finding it in KC because Lowes and Home Depot didn’t carry it and the lumber yards I called didn’t know it by the name Celotex. I finally found this material in a home center store named Menards. There are two types of this product one is brown like you see in the picture and the other is black because it is impregnated with tar. Stay away from the tar.
I built the target with a 2” x 6” base and top and put casters on the base. There are four sticks of all thread in each corner of the target that run from top to bottom that hold everything together. The top and the bottom (wooded pieces) act as a vise, by varying the tightness of the nuts at the top of the all thread I can adjust the compression of the Celotex. The tighter the compression the harder it is to remove the arrows.
I built a simple jig to cut the pieces of Celotex and a jig to drill the holes so that I would make all the pieces the same. The whole project took about a day to build and setup. And the only power tools needed was a skill saw and drill.
The material did leave a little bit of glue resin on my carbon arrows in the beginning but I adjusted the compression tension and the problem went away. The whole target cost in the neighborhood of $200 including the two 500 watt lights mounted to the floor joist, but the target is 6’ x 4’. Compare that to a Block Target 24” x 24” x 16” $209.
This target will last me for years and when I finally shoot out one side I’ll turn it around and start shooting the other side.
Good luck.