BowCast Blog

One of the bulkiest items on your gear list for a bivy hunt is probably your sleeping bag. If it has not been replaced in the last couple of years, chances are you can not only shave off some weight, but also significantly reduce the bulk. Almost all of the major sleeping bag manufacturers are offering sub 2 pound 3 season down bags now. Some have reduced the weight down to as little as a single poundand can be stuffed into a sack half the size of a nerf football. For my early season hunts in August and the first week of September I like a bag rated at about 30-35 degrees. Any later in the high country and you are increasingly flirting with the chances of sub-freezing temperatures. For those hunts I drop down to a 20 degree rating. Some of my favorite bags are from Western Mountaineering, Marmot, Mountain Hardware and Feathered Friends.

 

Down is graded by measuring how many cubic inches it takes to weigh one ounce. A 600 fill is 600 cubic inches per ounce. Several things to keep in mind as you shop for a featherweight bag is the higher quality the down, the lighter the weight and the better the insulation it provides. You should be looking for a minimum of 700-fill-power, with 800-900 being preferred. The difference between a 600 and a 800-fill-power bag of the same temperature rating can be over half a pound. The higher the number, the greater the loft and compatibility for the same fill weight.

 

For a 30-40 degree bag I'd recommend saving a few ounces and go with a half length zipper. Chances are you are not going to get too hot with the higher rating. If your budget will only allow the acquisition of one new bag, but your hunts cover the early August to late September time frame, I'd recommend going with a 20 bag with a full length zipper. You'll be a little warm in the earlier part of the season, but will be able to unzip to help regulate body heat. I made the mistake of sleeping in a 20 degree bag in Nevada with a half length zipper and roasted every night. Marmot has a bag that is rated at 40 degrees and only weighs a featherweight 1 pound. This would be a great bag for warmer climates in the early season. You can pack a long a set of silk or polypropelene thermals and buy a few extra degrees of comfort.

 

While you might be tempted to find a really roomy bag for greater comfort, keep in mind dead spots mean cold spots. The more contoured the bag the warmer it is going to be. Draft tubes, like baffled collars, help keep heat from escaping on lower temperature bags. Many of the bags are made in a couple or more different lengths so you won't have to be carrying any more weight than necessary. The shell of the bags are made from many different materials. Some are designed to save maximum weight, some for durability and others for maximum waterproofing.

 

The first thing I do when I buy a new bag is get another stuff sack one size smaller than the one provided. I've found I can reduce the bulk by at least 25% or more. Don't leave your bag in the stuff sack for extended periods as the down will eventually loose its loft and thus its insulating ability after extended periods of compression.