Hi jags!
Sea-to-Summit make some nice ones out of e-vent fabric (air squishes out, water doesn't enter...supposedly, but I am deeply suspicious of such claims over the long haul; such things tend to work well in shorter timeframes). Outdoor Research (OR) make some nice ones, too.
Some examples:
http://www.rei.com/product/730882/sea-to-summit-event-compression-dry-sackhttp://www.rei.com/product/766677/sea-to-summit-ultra-sil-compression-sackAnd now...a kindly meant caution:
If you're looking to compress the daylights out of your sleeping bag (or foam pad, for that matter) to save a *lot* of room, please be cautious -- it is possible to damage the lofting potential of the compressed items if they're squashed too much for too long, and it can result in longer camp setup at the end of the day while you're waiting for the bag to "reinflate". I tried this for awhile, and concluded it wasn't worth getting colder and colder while performing CPR on the bag, when it could have done the job largely on its own in the half-hour it took me to cook and eat dinner. First task for me on getting to camp is to set up the tent and open and lay out the pad and bag, shaking them well, then letting them fluff on their own. Usually by the time I've finished eating, the sun is setting and it is getting cold. Nothing is more discouraging than finding the bag is still flat as a
pannekoek (
http://en.wikipedia.org/wiki/Pannekoek I could live on that and some good, hot
snert:
http://en.wikipedia.org/wiki/Snert#Netherlands ) and the start of a colder than usual night awaits as a result.
I have decided to put my relatively light 'bag and pad in a dry sack atop my rear rack, so the lot can be a bit bigger without worry or bother. It sure has made a difference in bag longevity and readiness at the end of a long day, and if it is pouring, I just unstrap the dry sack and then remove the bag and pad directly from the sack into the tent while under cover of the vestibule. Makes the morning pack go more quickly for me, too, but there's a hundred ways to do it, everyone has their own pet method, and none are wrong. Most people I know seem to stuff their bags into their panniers, but I'm "different" in how I do things sometimes.
Overcompression can kill a synthetic bag amazingly quickly, and I have seen down bags' loft compromised over time by sustained over-compression. Some compression is fine, and for a relatively short period (say, the day's travel, rather than left in storage day after day), but it doesn't pay to overdo it.
A last caution, for those who wear contact lenses: Increasingly, sil-nylon is being used for rain lightweight rain gear, tents, dry- and compression sacks ("bags" tend to be thicker and heavier-duty than "sacks"). The silicone that impregnates such nylon transfers easily to hands and fingers, then to contact lenses, where it changes the surface tension and prevents tears from spreading evenly across the lens -- the dry spots can render even a fresh set of lenses unwearable. For that reason, I tend to avoid sil-nylon or wear some nitrile gloves when handling it. By the way, a study I read last year warned it can take 90 days or so for silicone to work its way out of the skin surface after handling, and contact lenses can be affected during this entire period.
Hope this helps, jags; I know you want to reduce your bulk, and that's a great and worthy goal.
All the best,
Dan. (...who thinks sleeping bags are a bit like people; they function well under a little pressure but tend to collapse under too much, sustained)
