Not too long ago, while in Alaska on assignment, I had occasion to spend a night or two testing a synthetic sleeping bag rated to 20 degrees. Granted it was raining, although the bag stayed relatively dry. Sure, I was tired from a 16-hour trek in chilly conditions. But feeling chilled at 35 degrees while inside the bag, even wearing dry Thermax underwear, dry wool socks, and a Polartec hat was not my idea of accurate temperature rating--this from a person who can regularly slumber comfortably at 10 degrees in a 20 degree rated down bag. What's up with temperature ratings?

According to Fred Williams, founder and past president of Moonstone, temperature ratings as they are currently used are pure bunk and should be abandoned.

"It is not all that uncommon to have users judge the minimum comfort limit of an identical sleeping bag up to 20 degrees apart. I know of at least one case where two users judged the same sleeping bag more than 30 degrees apart!" says Williams. "Even without the variables of environmental factors, clothing worn, food eaten, pads used, body size, fitness, etc., the perception of 'comfort' varies wildly."

"Testing instruments such as the copper mannequin provide clo data using a very controlled environment. The mannequin is a fixed size and does not roll. The comparative data that's collected is great for evaluating the comparative insulating power of bags used by the mannequin," adds Williams, "but how does it address the variables of body size (a small body in a large bag) or movement (nighttime rollers who constantly crush insulation), metabolism, and the other factors of the field?"

Gary Schaezlein, owner of Western Mountain Sports, manufacturers of Western Mountaineering down sleeping bags agrees with Williams wholeheartedly.

"We just try to be honest with what we are putting out and provide for our customer in the worst of scenarios, not the most optimistic," says Schaezlein. "In fact several years ago, we were copper mannequin tested and found our ratings were 20 degrees too warm--our 20 degree bag tested to 0 degrees for example. The bottom line with a bag is it must keep you warm."

Hallelujah to that! Moonstone also reports that they overfill their bags to ensure warmth. Wise field advise that I have heard dispensed over the years is that you can always unzip a bag if you are too warm, but you're going to have a problem trying to add more down or insulation if the bag's too cold. Of course, this doesn't mean you want to buy a bag that you will be sweltering in 90% of the time either.

One company, when asked how they were rating their bags, went so far as to state that they had their bags tested by the copper mannequin a number of years ago, and simply extrapolated the information into their current line.

Of course, those companies who choose to be more optimistic with their temperature ratings often come out ahead when you only catalogue-compare price, stuff size, temperature rating and weight. As any knowledgable retailer will tell you, as long as you know how to compare bags properly, temperature ratings are of little significance and merely serve as a starting point or a place of reference for the eventual purchase--hopefully an educated one.

The first word of caution from Williams is "don't get too caught up in the loft game because some insulations pack more insulating punch per unit thickness than others."

Indeed, tests conducted at Kansas State University indicated that a LiteLoft bag (no manufacturer listed) which had been abused until it had lost 27% of its original loft still managed to maintain 94% of its original insulating ability.

Because of all the confusion, a number of heavy hitters in the industry, including Cascade Designs, Sierra Designs, REI, Marmot and 3M insulations, have banded together to attempt to hammer out an unbiased, meaningful, understandable and standardized rating system. Don't expect anything to happen in the next year however, since not everyone in the industry agrees that standardized temperature ratings is a good or even achievable idea.

What, then, are the most important criteria to consider when buying a bag? Look at the foot section, hood area and draft tube. How are they designed? Are there any obvious cold spots? How do they compare with the other bag(s)? How much insulation is in the bag? Consider that bigger bags require more insulation to provide equal insulating qualities as smaller or more narrow cut bags. On down bags, do the compartments feel firm ( a good sign that prevents cold spots forming since down shift is minimized) or soft and fluid (a poor sign since the down is free to 'fluidly' move around the tube creating cold spots--only exception are those bags intended for the user to be able to shift down from top to bottom to adjust for temperature fluctuations).