Window treatment ---Recommendations on fabric?

I have a lot of windows in my listening room, floor to celing. I am going to put up curtains or fabric shades for absorption/reflection. I have covered the windows with other things I have around the house like blakets, towels etc. and the sound is better. I'm looking for your experiences or suggestions re fabrics/materials for this purpose.
I've found, generally, that either relatively thin cotton curtains or double "honeycomb" shades work the best. I have certainly not exhausted all materials, however.
High frequency notes will bounce off the glass, and be reflected back into the room (out of time, and phase). Low frequency notes will just pass thru the glass, possibly leaving presentation a bit lean (lacking bass). I can see how heavy theater type drapes might cut down on some of the high frequency notes hitting the glass, by absorbing some of their energy, but how do you keep the low frequency from passing thru. Would wooden blinds help keep some of the base energy in the room. It seems windows need to be treated for high frequency control, and low frequency retention. I have a 6 foot sliding door located right at the first reflection point on the right side of my new room. I'd love to know what treatments to apply to maintain the bass.
Thanks Dave
I'm pretty sure the Rives Audio website has some suggestions regarding your issue. The website is also pretty informative.

Dan S.
I have a lot of window area in my listening room and acheived very good results by treating my windows with Marigo VTS dots. I gained more focused and palpable images.
Hunter vertical blinds makes a Honey comb. It works quite well for some absoption and diffusion. For absorption heavy natural fiber of two different types, have a liner of heavey loose woven material like denium or wool and a lighter fabric on the outside. You need a gather of about 50% when the drapes are closed. This will work quite well. Short of replacing the inserts in the glass there is little you can do about the bass leakage.
Thanks to you all for the advice.