The lower the temperature rating, the more insulated the sleeping bag. A sleeping bag with a minus 10 degree rating keeps a sleeper warm in temperatures above minus 10 degrees F. However, if the temperatures dropped to minus 20 degrees, the sleeper would probably feel chilly. As another example, a 35-degree temperature rating means the sleeping bag would keep the sleeper warm at any temperature above 35 degrees F. If the temperature dropped to 20 degrees, the sleeper would be uncomfortably cold.
The type of bag you should choose depends greatly on the time of year you plan on camping. If you camp mainly in the summer, a sleeping bag with a rating of 35 degrees F or higher is ideal. If you camp in spring, summer and fall, a three-season bag is a better option. These bags have temperature ratings between 10 degrees F and 35 degrees F. If you camp mainly in fall and early winter, a cold-weather sleeping bag with a rating between minus 10 degrees F and 10 degrees F is your best option. If you camp only during winter or in an extreme environment, a winter/extreme sleeping bag with a rating of minus 10 degrees F or lower would serve you well.
Manufacturers assign temperature ratings based on the average person. Most people sleep comfortably at about 65 degrees F. However, if you pile on the covers at home, you're a "cold sleeper" and prefer a temperature above 65 degrees. As such, you should add 10 degrees to the temperature rating of all sleeping bags. Thus, a 20-degree bag would actually only be comfortable for you at temperatures of 30 degrees F and above. Adjust your selection accordingly. If you kick off the covers when you sleep, you're a "warm sleeper." The temperature rating is more likely to be accurate for you, so take the advertised rating at face value.
Women are usually more comfortable in warmer sleeping bags than men. Although men can assume that the temperature rating is probably accurate for them, women should add up to 8 degrees to the advertised temperature rating. Thus, a woman's sleeping bag with a temperature rating of 30 degrees F would probably only be comfortable at temperatures above 38 degrees F. Ladies should adjust their selection accordingly.
Some stores may use the European, EN Standard Ratings. Under this system, each sleeping bag gets four ratings. The comfort rating is the lowest temperature at which the bag provides a good night's sleep for an adult woman. The lower rating is the lowest temperature at which the bag can provide a decent night's sleep for a man. The upper rating is the highest temperature at which a man could sleep without becoming overheated. The extreme rating is the lowest temperature at which survival is possible.
