I have a StS Event dry bag. I bought one cause I needed something that also could slowly expand again while I had it packed to fill up the spaces in my backpack. So not the type with compression straps.. That's not needed with downgear, that compresses more than enough by hand presure.
I stuff downbag, clean clothes and liner into the drybag. Compress the lot by hand and stuff it completely below in my backpack. The space I cannot fill below gets'slowly filled by the slowly expanding dry bag due to the breathable Event membrame. BTW I use a 20 litre bag for 3-season or winterbag and then some clothes....
However lately I switched using my Exped pump bag that came with my downmat UL as dry bag. exped has also 'heavier' similar products like the Snozzle bag or the shrinkbags. They compress greatly without the weight of extra straps. However they don't fill op gaps in your bag by expanding slowly. I consider this bit as a slight drawback.
Edited: 07/05/2012 at 17:46