<o></o> I have read many posts on sleeping bags and have yet to get an understanding of how they are rated. <o> </o> Years ago, I slept in a bag rated for 30-degrees. In 20-degree weather, I felt like I was over heating. A few months later, I tried a friend’s sleeping bag, also rated for 30-degrees. This time I froze my butt off at 25 degrees. <o> </o> How does a company rate their bags? Do they just stick Joe Smo in a bag and toss him in a freezer? Is Joe Smo a skinny twig with not body fat? Maybe, Joe Smo is the size of a bear, all muscle, no body fat. Or, just maybe, Joe Smo carries around a lot of extra insulation. <o> </o> How long was Joe Smo stuck in the freezer? An hour or two, or longer? <o> </o> Did a computer or geek with a calculator perform a algebraic equation to come up with the number? <o> </o> What happens if Joe Smo, the computer, or the geek comes of with a golden number to be comfortable of 25-degrees? Do they round the rating to 20 or 30-degrees? <o> </o> I am in the market for a new sleeping bag, but want to make sure I am not buying a toaster over to melt away my extra insulation.