Help calculating sleeping bag system warmth

[Troy Ammons]

I have decided to return my Casper.

Decent bag but too tight for me. I have switched gears from a heavier bag and a light quilt to a lighter bag with a heavier quilt.

Inner bag will be a montbell SS UL down #5 that is rated for 40dF so I have some room to move around. Weighs 1#4oz

The quilt will be momentum .9 oz fabric with 5oz per sq yard, 1.2" loft climasheild XP. I will sew in a footbox, open almost to the end, with either an 12-18" zipper or some other fasteners.

Combo should weigh just under 3#.

Total top loft should be about 2.2" ??

I am thinking this should get me to an honest 15dF, but not sure. I know absolutely nothing about calcing CLO numbers and whatnot.

I will also be using a silk liner and an outer bivy if need be, probably made with tyvek.

I have also decided before my next winter hike to pick up a cocoon 60 hoody and pants.

I figure that clothing should add another 10dF

I sleep on a full length 3/8 blue pad (4 oz) with a thermarest small prolight on top. I might switch to a neoair later. Middle sleeper, IE not cold or hot.

So what temp do you guys think my combo would work at.

1. Quilt alone. I am guessing 35dF
2. IE montbell bag with quilt.
3. Montbell bag, liner, quilt and bivy.

Thanks in advance

[Joe Clement]

I bet the bag and quilt will get you to 0, and the quilt with a jacket and a baselayer would get you to 30 pretty easily. Did you think about getting a WM bag instead of the Montbell?

[Jim Colten]

1) quilt alone
Your quilt will provide 0.82*5=4.1clo
I have a 6oz Pl1 quilt, 0.84*5=5.04clo
that is OK for ME at 25*F,
with down booties, nylon pants, poly T, long sleeve scout shirt, unlined nylon windbreaker
no bivy
So 35*F might be OK (for ME) with your quilt

2) Quilt over the bag
I have been cozy at -13F in a 30*F Marmot Arroya topped by that 6Oz quilt and a 2.5oz XP quilt in a bivy
that is 7clo on top of a bag that was fine for ME at 30*F
From that experience I might hope that your 4clo quilt would extent a bag's rating about 25*F (for ME)

3) with liner … no experience with liners, sorry

[Troy Ammons]

0 sounds good. I have read about people taking the montbell SS bags down about 20dF below what is advertized with extra clothing and whatnot.

Gees I have looked at them all over and over.

Problem is there is nowhere around here I can climb into
one of these higher end bags.

I am also way out of the loop. Been using my old snow lion and kelty, Eureka gear for many moons. When I bought those older bags everything was loft with honest ratings, and I sort of had an idea of what would work where. Now its R values via clo and some crazy overstated ratings like the pounder.

My tent died a miserable death and its too heavy anyway. My synthetic 4# bag has delofted a bit, but it took 20 years. Its still a good bag though, it just went to a 45dF bag from a 35.

My old 4# down bag is still superb, but a little too short for me. Should be though it cost something like $500+ back in the 70's.

All in all it was just time for a major upgrade to lighter and better equipment.

I had a Montbell synthetic burrow bag that I returned. Got a right zip for some unkown reason, but I did like the extra flexability and room.

Thought this combo might work. The price was decent at prolite, so I guess we will see. The #7 UL 50dF long was even cheaper at $188, but this #5 is a bit warmer and only slightly heavier. I think it was $203 which I thought was a good price.

Now I just need to make the quilt.

I have a jam2 pack but I am Still working on my old Kelty pack. In 74 it was considered light then, and by todays standards its still not too bad for an extra large internal frame pack. Got the zippers working, I have stripped off some of the non essentials, sewing on some more outside pockets and loops, I rebuilt the shoulder straps, changed the metal adjsters and clips to plastic, changing the bottom sleeping bag divider to a clip type, use it or not, Same with the top center divider. Also going to make a carbon fiber frame to replace the heavy aluminum frame.

Should come in at 2.5# when I am finished.

[todd]

Troy,

FWIW, the system below was WARM at 19*:

JRB No Sniveller
MB 120 pad & pillow w/CCF sitpad under feet
Equinox bivy for a little added warmth
MB Thermawrap Parka
Polyester (thin) base layer
Smartwool 1/4 zip mid-wt top
Smartwool socks
shelter was a Gatewood Cape
JRB Down Hood

the system is very versatile, and, assuming you take an insulating top at low temps, should be less bulky and lighter than a two bag/quilt system w/insulating top. I also carried, but didn't use, a UL windshirt which I have draped over the foot end before for warmer feet.

Todd

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