Owens Corning 703 or 705 are the material that most select, as it is easier to work with than some other products. For corner bass trapping you want to use at least 4" of material, you can double up 2" material. Most straddle the wall/wall corners and wall/ceiling corners. First reflection points are for mid/high freq's so 2" 703 or whatever is fine, they are used to reduce the redundancy of the same signal hitting your ears at different intervals, which reduces clarity and imaging. Filling the entire corner will give you yet better bass trapping, that is called superchunks where you cut the 703 into triangles and fill the corners. This takes more material to go from floor to ceiling, but will give you better absorption. Keeping the first reflection points material off the wall somewhat aids in giving you better absorbtion. Here are some links that helped me, including a thread on this forum showing some of my construction. I also have pics on my website.
http://www.axiomaudio.com/boards/showflat.php?Cat=0&Number=144818&an=0&page=0#Post144818http://www.ethanwiner.com/acoustics.htmlhttp://gikacoustics.com/http://www.radford.edu/~shelm/acoustics/bass-traps.htmlhttp://www.audioholics.com/techtips/roomacoustics/DIYabsorbersacoustics.php
