Here is what I am looking at... two bags very similar in specs but the BA has the entire fill on the top of the bag the GoLight has it on top & bottom. That means there is twice as much on top of you in the BA, than you would have in the Golight.

There is an ounce more down in the GoLight but it's in the hood which the BA does not have.

How could you be as warm in both if you are sleeping on a pad with either???

Big Agnes Pitchpine 40° Sleeping Bag
Fill Type 800 fill goose down
Fill Weight: 10.5oz
Bag Weight: 1lb 2oz
Shoulder Girth 67.5"
Hip Girth 64"
Foot Girth 43"
# Shell Fabric: Pertex Quantum rip-stop nylon. Featherweight, high thread-count fabric that is soft as silk with a small packing volume. WR surface treament to repel water
# Lining: Ultralight, high thread count, soft nylon taffeta

GoLight Adrenaline 40° Sleeping Bag
Fill Type 800 fill goose down
Fill weight: 11.6 oz / 330 g (Men's regular)
Bag Weight: 1 lb 9 oz. | 540 g
Shoulder Girth 60"
Hip Girth 47"
Foot Girth 39"
50/50 distribution of insulation for full loft and warmth for side/front sleepers
20 denier ripstop nylon shell with
DWR Silken 100% polyester 22 denier micro fiber liner Pertex® Endurance

Edited by ctracyverizon on 03/10/2011 05:27:18 MST.

Great question.

I'd say they can't! (Except in rare circumstances, or so someone after me with a greater educational background will point out!)

I was talking with a someone I was transferred to at BA about this and they could not answer that.

They are going to have one of their design engineer’s call me back. She said she
is interested in knowing as well.

She said all of the manufactures go through the same industry rating tests to determine temps.

But... how 5oz on top of you and 5oz underneath, could be as warm as 10oz on top of you she could not say.

(Update) So I got a call back from BA and they looked at the specs from the GoLight site and said that the smaller volume of the GoLight bag would have an effect on the rating but other than the difference in volume they could not explain much about how the ratings could be the same.

Any smart folks here have an opinion?

Edited by ctracyverizon on 03/09/2011 09:54:37 MST.

There is no industry standard test for rating quilts or top bags.

Edited by simplespirit on 03/09/2011 09:52:11 MST.

That's interesting. Not that I would know, but she went into depth about how the test was conducted and what was worn as a base layer for the test.

That was gross misrepresentation on her part if they don't actually do that as part of what she called an industry standard of testing that "ALL" manufacturers do for rating their bags.

Edited by ctracyverizon on 03/09/2011 10:02:29 MST.

That sounds like the EN testing, but I'm fairly certain it only applies to traditional bags with insulation on the bottom.

Edited by simplespirit on 03/09/2011 10:05:20 MST.

The bottom insulation is compressed by your body and eliminates much of the insulating airspace therein.
Moving that fill to the top essentially doubles the loft in the area of greatest potential heat loss.
It now traps more of that rising warm air because there is more insulation(dead air space) up there and less heat is lost to the outside air over a given period of time.
What i have found in practice is by using the same pad (ridgerest closed cell foam) with a sleeping bag and a quilt is that losses due to conduction with the ground are seemingly the same. The ground does not feel any colder under my quilt.
there is something to be said for the way the bottom of the sleeping bag thats not under compression fills the unused internal volume of the bag and reduces the air that needs to be heated. This can be overcome by filling the spaces under the quilt with clothing.

What get's me at this point in what I am finding out is that for the same amount of fill above you in a mummy bag, you have to pay a lot more.

I other words to get a bag with 10oz of fill on top of you, with a mummy bag you have to buy a 20oz fill bag. So you have extra cost, weight and size.

I am starting to see how much advantage there is in quilts.

1) You are not simply cutting the bottom half off of of a bag to make a quilt. In my opinion, if you take a bag and cut out a 3-4 ft section ~1ft wide (and lose the hood) the tucked quilt will provide the same amount of internal space as the original bag. This may amount to losing 20-30% of the bags volume definatly not 50%.

2)I don't know about the rating on the golite but it is a woman's bag. I have noticed different ratings for men and women -- this makes since as women typically need more insulation. The golite for you might be a warmer bag.

3) The total area over which the down is lofted should be about as important as the amount of down in determining a warmth rating

when you say "similar specs", were you only looking at the specs you listed? Because the obvious difference I'd look for is their size -- length, girth. BA bags are typically pretty girthy while a golite women's bag is probably much shorter and narrower.

A couple of things to consider that might account for the same rating if the same test was used to determine it.
-Just because there is 10oz of down in the bag doesn't mean it's evenly divided between the top and the bottom. They could put less in the bottom because they know it gets compressed (unless they told you it's evenly filled and the down in held in place, ie. not continuous baffles).
-Maximizing loft doesn't mean putting as much down as you can into an area. So if overstuffed while the loft is maxed out isn't going to get you much additional warmth right away (though as you lose feathers overtime the rating should stay pretty constant).

If I'm misunderstanding either of those reasons please correct me.

> She said all of the manufactures go through the same industry rating tests to determine temps.

Oh Yeah?
If they can't display an EN certificate then who knows what 'test' they are using?

This has been a problem with AMERICAN sleeping bags for decades. There are very well documented examples of American ratings being up to 15 C (27 F) higher than they would be if tested in Europe. The rest of the world simply ignores American ratings these days, unless they have an EN certificate.

Cheers

I realize that the cut of the bag, the volume etc. will make for less space to heat.

But keep in mind that the weight of both bags are about the same and so is the fill weight. If the material weight of the bags is not much different then I doubt that the volume would be.

I can't imagine there is much difference in heating area with someone in the bag.

I added to the available specs and now show that GoLight does a 50/50 with half the fill on top and half on the bottom to accommodate front or side sleepers so there it is that you only get 5oz of fill on top vs 10oz on top for the BA.

GoLight Does not list their girth.

This is not a stomp on GoLight by the way just a search for warmth, value & weight.

If your pad will keep you warm why pay for or carry the weight of fill under you.
I am not considering winter bags here just spring through fall.

Also, I just don't get how these bags could possibly be rated the same in truth.


Big Agnes Pitchpine 40° Sleeping Bag
Fill Type 800 fill goose down
Fill Weight: 10.5oz
Bag Weight: 1lb 2oz
Shoulder Girth 67.5"
Hip Girth 64"
Foot Girth 43"
# Shell Fabric: Pertex Quantum rip-stop nylon. Featherweight, high thread-count fabric that is soft as silk with a small packing volume. WR surface treament to repel water
# Lining: Ultralight, high thread count, soft nylon taffeta

GoLight Adrenaline 40° Sleeping Bag
Fill Type 800 fill goose down
Fill weight: 10.9 oz / 310 g (women's regular)
Bag Weight: 1 lb 3 oz. | 540 g
50/50 distribution of insulation for full loft and warmth for side/front sleepers
20 denier ripstop nylon shell with
DWR Silken 100% polyester 22 denier micro fiber liner Pertex® Endurance

Edited by ctracyverizon on 03/09/2011 14:22:10 MST.

Is Pitchpine a quilt? I thought it just a regular hoodless mummy bag with bottom insulation.

The Pitchpine is a top bag. I was not considering quilts in this thread just the ratings of the two bags listed and how that bears on ratings for Sleeping Bags against similar rated Top Bags. (I am not into quilts yet but I am on my way!!)

Edited by ctracyverizon on 03/09/2011 14:44:10 MST.

I think you have a few factors here.
First, since neither manufacturer uses EN ratings there is no standard, and the ratings can be very different from different manufacturers.
Second, the specs on the two bags may be further apart than you suppose. I note that there is no girth dimension mentioned in your post for the golite bag and I couldn't find one on their website either - just a reference to a "thermally efficient taper, the Golite Mummy Fit" . Big Agnes bags tend to be wide - as the 67.5" shoulder and especially the 64" hip numbers confirm. If the golite bag is significantly tighter, say the size of a WM ultralite at 59" shoulder and 51" hip, then that makes a big difference in how much bag that down has to fill, plus makes a warmer bag by being tighter. Top bags are not 1/2 of a mummy bag - they are more like 3/4, since the insulation needs to come down the sides as well as over the top.

Add up all this stuff and then you can see that the difference isn't as big as it seems at first glance. So it's likely that there is nothing like twice as much down on top of you - the difference would be quite small.
If you could put your hands on both bags and measure the loft, that would be interesting info.

"But keep in mind that the weight of both bags are about the same and so is the fill weight. If the material weight of the bags is not much different then I doubt that the volume would be."

I don't really understand your logic. In anycase, there's a huge difference between the surface areas of the bags. You're comparing a "regular" bag to a women's bag which is usually a 6" length difference to start with. And then the girth difference is significant.

Shoulder/hip/foot girth (in inches):
BA - 67.5 / 64 / 43
Golite - 54 / 42 / 36

So, even if only half of the BA bag is filled, the filled area is closer to the total area of the Adrenaline than you might think. If you estimate the distribution of the down in terms of ounces per square area, it'll be pretty darn close. And it's that metric that mostly determines loft and density, i.e. warmth.

I think the post above makes a very good point that the surface area isn't really all that dramatically different between the two bags. I think there are other differences as well that have a lot to do with the temperature ratings vs. weight.

The Big Agnes bag does not have a hood, thus it would require more loft to compensate for it's lack of coverage.

The Big Agnes has much more girth, and this means that it has more space inside to heat. If temperature ratings are based on the same size person, than a roomier bag will need more loft to achieve thermal equilibrium at the same temperature.

The Golite Bag appears to be of baffled construction. The Big Agnes appears to be sewn-through with a lot of stitching lines. This construction uses down less efficiently.

It really is an apples and oranges comparison, especially given that one bag is women's model and the other unisex. They would be quite different to sleep in as well I am sure.

Ok ... there are some really good points being made.

I had not considered the construction of the two bags and the design efficiency of sewn through vs. baffled … and having your head inside the bag with a hood adds a lot of heat.

I was able to find all the specs on the GoLight Bags and updated the comparison to a men’s regular.

http://www.golite.com/Product/ProdDetail.aspx?p=160005110&mc=&t=&lat=

Big Agnes Pitchpine 40° Sleeping Bag
Fill Type 800 fill goose down
Fill Weight: 10.5oz
Bag Weight: 1lb 2oz
Shoulder Girth 67.5"
Hip Girth 64"
Foot Girth 43"

GoLight Adrenaline 40° Sleeping Bag
Fill Type 800 fill goose down
Fill weight: 11.6 oz / 330 g (Men's regular)
Bag Weight: 1 lb 9 oz. | 540 g
Shoulder Girth 60"
Hip Girth 47"
Foot Girth 39"

Edited by ctracyverizon on 03/10/2011 05:19:58 MST.

unless the bags are en-rated .... you might as well make up a number ...