Also, have a look at ReadyAcoustics stuff. If you're willing to spend a few bucks, the ReadyBags look like a great DIY alternative. For the ease of installation and finished look they're a pretty good value.
check out the ready acoustics stuff. you can buy the bags from them and put them together yourself. really easy and it came out cheaper than building my own. just humg them with string and zip ties. follow link to see pictures of finished product. https://www.gearslutz.com/board/low-e...reat-room.html
I built mine out of 1 x 4 pine and owens corning 703. SPI (just do a google search for SPI acoustics) sells 703 and 705 in 2 x 4 pre-cut panels. If you want to glue two together to make a 4 inch thick panel, you can just use liquid nails for foam board around the perimiter of the 703 and glue the two pieces toether back to back. Don't coat the panels with glue though, just around the edge.
Its best to hang them from the ceiling on wire (I used suspended ceiling wire at H.D.) and eyelet screws (also for suspended ceilings). Then you can space them off the wall, which will help your bass response. Mine are 4 inches thick and are 4 inches off the wall.
You can also find fabric on E-bay. Be careful with fabric through, you want something that you can blow through so sound will pass through as well. Some fabrics will be reflective, which defeats the whole purpose.
6" 703 will has a sabins COA pretty flat down to 60hz. Burlap makes a great covering and is dirt cheap.
I mounted mine with a wood bracket 45 degree receiver screwed into the wall and a matching 45 mounted to the panel. The panels simply hang there and can be removed at any time by lifting. Here's a crude drawing.