Bushwalk Australia

The compression dry sack manufacturer claims that it saves space and keeps your gear dry.

Any thoughts - we were thinking of getting one for our sleeping bags.

I do like to not compress my down bag too much. I have read some research that everytime you overcompress a down bag it looses some insulating value. I never use the usual small bag to stuff my bag during a walk and store my bag uncompressed at home.

I'm the opposite. I compress the begeesus out of our bags, and also have a compression sack for our clothes.
Saves a lot of space.
Never noticed any side effects of degredation in the bags. The down in our bags is 95% superdown, and it recovers well.
When the tent is set up, we inflate the thermarests then put the bags out, they fluff up nicely in not much time at all.
As for keeping things dry, well if the weather is at all questionable, or if there are river / creek crossings to do that mean wading, our sleeping bags as well as our clothes compression bag will each have their own plastic garbage bag. I would not rely on the compression sacks to keep things dry, even if inside the pack with a liner in the pack as we use.

Thanks for the feedback guys - all food for thought.

If you use a pack liner and wrap your items in large garbage bags you can keep your gear dry. Years ago (1974) we lilloed partly down New River to save scrub bashing, and used just garbage bags. Even though our packs were sitting partually in water we had no problems with anything getting wet.
Keith

Having a re-read of this, I do agree with under10kg in that it is important to store your bag uncompressed at home. You find all about that when you buy them.

When we swam across the Franklin at the Irenabyss a couple of years ago we had pack liner bags inside the pack, our clothes compression sack and our sleeping bags were each in separate garbage bags as was our camera gear, and we put our packs each in their own big orange garden type garbage bag... Tied them up and tied a line to them and I swam across first, my wife placed them in the water and I pulled the line across - they floated across effortlessly (pull quick so they don't get downstream of you coz then you're pulling against the current). Point is, we went to way too much trouble to keep things dry, as hindsight showed, but to us it wasn't worth the risk.
Two things in your main post - waterproofing and compression. I think I have covered my views now..........

My comments on down loosing loft from repeated over stuffing are based on my own experence. Do you remember that your new down sleeping bag was so warm when new and after a few years of use it is not so. Long distance walkers who do 3 or 4 months trips also have noticed that the down bag looses some of its loft from repeated ovestuffing.