Quite a few bags should meet your criteria, Mike. Moreover, most bags today are made with some sort of water-repellent material, which greatly reduces the problem of bag wet-out that was fairly common 20 or 30 years ago.
Allow me to offer some definition of terms as well: Ripstop" is a generic term referring to a fabric construction that uses reinforcing cross-stitching on a lighter material. The cross-stitches help prevent small tears from growing into big tears, hence the name. Pertex is a brand for several fabric products, including Quantum (a super-light material) and Endurance (a two-layer, highly water-resistant material used in some sleeping bags).
So if water-resistance is your priority, there are several options. One excellent bag is the Exped Ibis WB ($369; www.orgear.com), a bag rated to 18 degrees F that combines 700-fill down with a Pertex Endurance shell. Its warm, soft, and nearly impervious to the kind of moisture that usually gets to down bags, such as drips from the tent door, condensation, snow dragged in by your tent mate.
I also like the Feathered Friends Swallow (www.featheredfriends.com), which for years has been perhaps the best 20-degree bag on the planet. Its available with two shell options: highly water-resistant Epic Nextec ($349), which employs silicon-coated fibers; and eVent ($404), a two-layer waterproof-breathable membrane. Keep in mind the eVent bag is not totally waterproof, because the bag still has seams. Overall, I think youd see the best performance in the Epic bag, although if youre really around damp conditions a lot, the eVent bag is worth a look.
Lastly, you can go with a bag that has a shell made with Gore DryLoft, one of the first materials expressly designed to keep insulating bags and jackets dry without sacrificing breathability. Its not waterproof, but it is highly water-resistant. Western Mountaineering makes a beautiful DryLoft bag called the Apache Super DL ($445; www.westernmountaineering.com), which is rated to 15 degrees. Western makes the same bag with a polyester microfiber for $365. I personally like the microfiberits softer than DryLoft for better drape, dries in a flash, and is inherently water-resistant.
I honestly dont think youd go wrong with a single one of these bags. Theyre all well-made, warm, and work well even in damp conditions.
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