I was on a caving trip this weekend, but we camped outside the cave during the nights, and it was raining all weekend, thats three nights of rain. I brought all synthetic insulations on this trip and now have a greater appreciation for their ability to keep you warm when wet. It was about 35 degrees each night+-. and I wore under armor cold gear top, polyester tights, polyester compression shorts(underwear),a fleece beenie, fleece socks, and a cocoon jacket. inside my 50 degree mont bell clo-up sheet, and I was warm enough. I also had a fleece vest, but did not wear it while sleeping, but did in adition to my under armor, fleece hat, and nylon pants in the 50 degree cave

any way, I was thinking when I got back, I would rather have synthetics all the time, and I was confused as to how they are so heavy. So I went to thru-hiker.com and checked out what they had to make a sleeping bag. I guessed that for an arc bag, you would need less than 5 yards of fabric. thats only about 5 oz with .9oz fabric but I added an ounce for webbing, draw cord and toggles, that means only about a 6 oz shell for a bag without baffles. and for insulation you only need about 2 yards. and I found some 1 inch thick climasheild HL for only 2.7oz a yard, I rounded to 3 oz a yard X 2 thats six ounces for insulation. thats a 12oz(probably less) synthetic 40-45 degree arc bag.
I guessed on this temp rating of 40-45 for a 1 inch loft
why is this not made by a big company?

or even warmer bag with 2 layers of climasheild HL thats 1.5-2 inches of loft
so you need 4 yards instead of 2 and the 6 oz shell
2.7 X 4= 10.8
10.8 + 6= 16.8
thats a 30-35 degree synthetic bag for a pound
Ray jardine says 2 layers of .9" synthetic is rated 28 degrees

am I missing something here?
sounds good to me.

Edited by ryanf on 04/10/2006 11:51:23 MDT.

Why's it not made?
Cause it will weigh more than your estimate. You're lowballing the fabric weights, seam allowance costs, etc. "Actual finished weights may vary."

This is not to discourage you. Make the thing. In fact make 2 or 3 with different thicknesses. Put the second layer in the middle and leave 6 to 8 inches around the sides with only one layer. It tucks under easier and the extra layer isn't needed there anyway.

And Jardine lowballs the amount of insulation you need by about 1/2 inch according to most manufacturers' ratings. 0.75" might be 45F. But I'd use 0.9" my ownself. But I think 2 layers of 0.9 might get you to 32.

Yeah it may weigh more than I think, but probably close, the yards are 60" wide and I would need 55" max
and the climasheild says .75"-1" loft
so I think one layer would be good to 45, and 2 to 32.
I will be getting a sewing machine soon, I will make up a proto and then a 45 degree synthetic arc hopefully under 13oz.
and a 30 hopefully under 17
but I think because I will probably not need the whole widths, I will be close to my estimations of 16oz and 12oz

Edited by ryanf on 04/10/2006 12:20:40 MDT.

I have heard of a BMW Arc cocoon coming up, anyone have any info, I am guessing that it will be pertex quantum and PG delta.

anyone have any more info?

The weights listed for material and insulation are normally per square yard...not a running yard , which is how it is sold....so recompute the material requirements with all seam allowances, get to the sq yd at two or more decimal places then multiply the weight...BTW, read the small print on fabric weights....For example: the 0.8 taffeta advetised on Thru-hiker is 0.9 when you click on that page and when you read the text it states it has a weight of 1.05....

Pan