Loft to Temperature ratio?

[JohnSawyer]

Differential cut UQ's take int account that the fabric against the hammock should be shorter than the lower fabric on the UQ, as the fabric wraps around the bottom of the hammock.

Differentially cut is more efficient, as you're not compressing the down, as the outer shell isn't pulled tight....

For example: against the hammock, the baffles might be spaced 5" apart, where the outer edge might be spaced 5.25"...

[HappyHiker]

I used this chart as a rule of thumb:
http://thru-hiker.com/projects/down_quilt.php

Consider the loft on the chart as baffle height instead of just loft, as the loft will vary depending on cut and fill. That, and the baffles will be the minimum loft on your quilt so go with those as the minimum. These values pretty much match what the cottage guys are putting out as well. See https://docs.google.com/spreadsheet/...EE&hl=en#gid=0 for comparison.

Differential cut simply means the outer cover is cut longer and wider than the inner to prevent compression of the down. You increase the baffle spacing on the outer to account for the increased width of the fabric.

Also see http://www.hammockforums.net/forum/s...d.php?p=553311 which has the UQ calculator: https://docs.google.com/spreadsheet/...hl=en_US#gid=0
It's a great place to start figuring baffle heights, differential and required fill.

HTH

[Living the Highlife]

Ok. I guess I didn't really think about a differential cut just because all the plans and threads that I've been looking at, the shell and outer layer are the same cut. I'll have to look at those links, cause my iPad is not working with google docs. I appreciate the help everyone! This TQ and UQ will be epic!

[BillyBob58]

That Thru-hiker chart seems to agree with JRB quilt ratings. The MW3 has 2" baffles and 3" loft and is rated 15-20. The MW4 has 1 more inch of baffles and loft, and this buys you another 15F of warmth, for a 0- +5 rating.

[Living the Highlife]

Well I'm glad everyone is feeding me the same story. I start really judging my work when one says one thing and another person says something else right after I get it off the sewing machine.

[DemostiX]

With all respect, the differential cut reduces weight by having the chambers more optimally shaped for volume relative to baffle and inside fabric required to do it. Obviously, folds and pleats on the inner surface don't contribute anything but weight.

But, down compression? Nope. If down compression were an issue, you could just put less down in the chambers. And there is much belief that while loft is a main contributor to insulation, so is the down, and not just to stop convection.

Differential cut because it looks cool and undoubtedly optimizes. Just how great the value of the insulative optimization is would require testing. Weight and fabric savings should be straightforward to calculate.

[Bitts]

Another thing to throw in the mix. Is that the combination of top & bottom insulation will have a huge impact on the overall performance. All sleeping bags are rated for a "set" temp, but only when used with an equally rated pad/UQ. That -40 bag does almost nothing for you when your back is exposed to the cold. I've taken a 0 degree bag to almost -30, but frozen my tail off in the same bag in the 30/40s because of this. (note to self: blue foam pads don't pop)

[Living the Highlife]

I used this chart as a rule of thumb:
http://thru-hiker.com/projects/down_quilt.php

Consider the loft on the chart as baffle height instead of just loft, as the loft will vary depending on cut and fill. That, and the baffles will be the minimum loft on your quilt so go with those as the minimum. These values pretty much match what the cottage guys are putting out as well. See https://docs.google.com/spreadsheet/...EE&hl=en#gid=0 for comparison.

Differential cut simply means the outer cover is cut longer and wider than the inner to prevent compression of the down. You increase the baffle spacing on the outer to account for the increased width of the fabric.

Also see http://www.hammockforums.net/forum/s...d.php?p=553311 which has the UQ calculator: https://docs.google.com/spreadsheet/...hl=en_US#gid=0
It's a great place to start figuring baffle heights, differential and required fill.

HTH

thanks for all the awesome links!! Do you use the same Differential cut thought process for constructing a TQ? or does that only apply to UQ's?

[DavyRay]

thanks for all the awesome links!! Do you use the same Differential cut thought process for constructing a TQ? or does that only apply to UQ's?

I think this depends on the shape of the item in its intended use. A mummy sleeping bag is pretty much round or oval in use. It is obvious that the outside has to be larger than the inside, or the down gets compressed. An UQ for most hammocks will be definitely curved when in use. Also the tension applied to the upper fabric should not be applied to the under side fabric.

For a TQ, it is not so important. The TQ is curved around the person somewhat, but not too much. The TQ is probably not pulled or stretched in use, so neither surface is tensioned.