Sleeping Bag Ratings - A New Idea
By Steve Gillman
Sleeping bag ratings seem have no consistency. I'm talking
about the temperature ratings, which are still determined entirely
by the manufacturers selling the bags. My 3-pound Sierra Designs
bag was rated to 20 degrees, but honestly, it never kept me as
warm as my 17-ounce Western Mountaineering sleeping bag, which
is only rated down to 40 degrees. This is a problem when you
buy a bag, isn't it? Will the bag that says 30 degrees really
keep you warmer than the bag that says 45 degrees?
How to Have Consistent Sleeping Bag Ratings
First of all, no matter what temperature a bag is rated for,
under any system of testing, it won't necessarily keep you warm
to that temperature. We can't solve the problem of people having
different bodies and metabolisms. The same bag might be good
for one person down to 20 degrees, while for another it is only
good to 40 degrees. You generally can figure out if you are a
cold or a warm sleeper.
The best we can hope for is to know that if a bag says 30
degrees it will keep you warmer than one that says 40 degrees.
Then, even if you need to add or subtract 10 or 20 degrees for
your personal tastes, you can still figure out which bag is the
warmer one. So how do we get this consistency?
Start with any bag. Put a bag of water in it that is human-sized,
weighing perhaps 160 pounds. Maybe have three standard sizes
for small, regular and large sleeping bags. Start with the water
temperature at 100 degrees Fahrenheit, and measure how long before
it drops to 90 degrees. The external air temperature has to always
be the same too. It might be set at 60 degrees or 40.
These numbers are not crucial. What is important is that once
the standards are chosen, every bag is tested the same way, with
the same conditions (even the temperature and material of the
testing platform would have to be the same). That is what will
give consistency to the sleeping bag ratings for warmth.
If a bag rated to 40 degrees keeps the water above 90 for
two hours, a bag rated for 30 would obviously have to keep it
above 90 degrees for a longer time. The pegging of heat-retention
times to specific temperature ratings would be a bit tricky at
first. Once done, though, each new bag on the market could be
submitted to the testing and quickly given a consistent rating.
You would know that a lower rating would always mean a warmer
bag degree-by-degree. You could even have old bags tested to
see if it is time to replace it.
What if a company started doing sleeping bag ratings this
way? Would the manufacturers pay to submit their bags to the
tests? It would be a an advantage for those companies who are
already conservative in their temperature ratings. Then they
would have "proof" that the bags are even warmer than
they were claiming. Eventually, all bag makers would feel some
motivation to have their sleeping bags tested, because consumers
would be wary about buying ones that weren't tested.
Hopefully someone will take this idea and run with it. Maybe
an existing rating company, like consumer reports, could do this
on their own and report the results. Even if they just listed
the bags without temperature ratings, but in absolute order of
which held the heat in the best, it would be very useful. You
look at the list and if your current bag keeps you warm to 25
degrees, you know that any bag above yours would be warmer. It's
time for consistent sleeping bag ratings.