Sorry for the delay in responding, somehow the "new posts" search failed me..
Anyhow, YES, the bags generally are constructed of a cloth-like material on the sides that allows water and nutrient exchange with the surrounding soil. The bottoms are a fused or glued plastic material of some type that prevent deep tap-rooting(by forcing them to grow horizontally into the fabric sides).. When the roots reach the fabric they begin to grow through it and then are choked out because the fabric does not give, thus constantly pruning them in a non-stressful manner.