Quilt warmth of a single layer of 1.8 primaloft.

Just a thought, but I made a similar quilt out of 2.5 Apex that weighted in at 13oz and could go to about 45.

If you could find your hands on some of that, it might be easier to use and nearly as light. I believe I heard that thru-hiker hopes to get more this spring.

3 oz primaloft is about 2 clo

so 1.8 oz would be 1.2 clo

1.2 clo would provide about 75 F lower sleeping comfort limit if you were naked inside

What are you wearing inside?

"1.2 clo would provide about 75 F lower sleeping comfort limit if you were naked inside."

Ah Jerry, now you've done it – you've gone ahead and introduced scientific values that help destroy marketing hype. ;|

To the OP, you might consider searching some of R Nisely's older clo value threads. In essence, you need a clo value of around 3.25 to be comfortable sleeping at 55 degrees F, and, as Jerry notes, around 1.2 to hit 75.

Interestingly, you only need a clo of around .8 (ie dressed) to be comfortable **sitting** @ 70-75. That means you're burning approx 1.5x as many calories sitting vs sleeping.

For those considering Sierra summer bags, 30 is the usual target range since it can (and does) dip below freezing even in August @ higher elevations. 30 requires a clo of around 6.5, which loosely translates to around 7.5 oz of syn or 2.2" of down loft. (Hence the 2" of loft [one side] in the 32 degree WM summerlite.)

Good Richard thread:

http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/9378/index.html

But, I think maybe it overestimates the required amount of insulation a little

Richard's values are definitely conservative but accurate. This is probably because they're based of EN standards and they are designed to be accurate for a majority of the population, not just the average or median values (ie those clo values should work for 90% or so of people).

Also I think the linear regressions lose a lot of accuracy when temperatures are warmer, like 45F and above. But regardless the error still falls on the side of conservative so at worse you'll just end up with gear that's comfortable even colder than you intended!