Originally Posted by
BillyBob58
That is a darn good question. I have noticed over the years that many bag manufacturers seem to consider a change in loft of 1" ( total, top/bottom) to be equal to about 10° warmth. I notice that your two examples have 1/2" loft diff and have 5° dif per WM's rating. Now that is with no baffling confusing the issue. Although, at the WM website, it shows the Megalight has actual baffles, and is not sewn thru? Is yours an older model that was sewn thru? If so, it just makes the comparisons a bit easier, because the baffled model at their web site still is rated for 4" loft and 30°. So, 1" loft dif still makes 10° dif ( or in this case 1/2" still = 5°), with or without baffling being added to the warmer model.
As you go down the list at the WM site, with other models that are baffled, the pattern holds the same. As long as features like collars and girth are accounted for, in the same "series" of bags- 1" loft seems to make the same 10° dif in the other bags baffled or not.
The sewn thru Linelite has 2.5" loft ( 1" less than the 35° highlite) and is 10° cooler at 45°, though intended to be used as a liner where lack of hood would not effect the rating so much. A Tamarck WITH baffles is 4" and 30°, just like your Megalite. The baffled ultralite Super is 5"=20°. Adding 1" loft PLUS baffles still made only 10° dif. The Versalite Super is 6" and 10°, with baffles.
Again, sleeping bag size, fabrics and construction can all make a 5-10° dif at the same loft. But I'm starting to wonder exactly how much baffles really contribute to raw warmth rating, as opposed to just giving better control of down and more consistency. I always thought it made a big dif, but now I'm wondering. Though importance of control of the down is not to be dismissed.
Here is another question to go with your original questions. How much do baffles weigh, and how much does adding them to a bag cost? In other words, a sewn thru bag with an extra 2 ozs of down vs. a baffled bag with less down- which would be warmer in the field, or weigh less or cost less, with all other things equal?
I figure there is someone here who knows the answers.
Bill
Bookmarks