DIY UQ Question (air gaps)

**rstetz** · 05-19-2015, 09:15

A friend and I are making down UQ's with baffling. In my research, I saw a couple people used a smaller piece of ripstop on the top than on the bottom so that it hugs the bottom of the hammock more. I was just wondering, is this all that important? Does it really make a big difference or as long as your ends are cinched well enough, there won't be any air gaps? If it does, how much smaller do you make it? We're at 58" wide right now (for bottom piece) leaving an inch on each side for roll hems, bringing the total width to 56". We're going to have 6 baffles separated 8 inches from each other creating 7 channels for the down. And advice?

Thanks in advance.

**Boston** · 05-19-2015, 09:59

This is known as a differential cut. The reason this is done is to avoid compressing the down when the under quilt is snug. It's pretty much necessary for an under quilt to work the way you expect. In the early days of hammocks people didn't do this, and had a lot of problems with quilt performance. No body i know of sells a quilt that doesn't have a differential between the shell layer's.

You can find my mod of CatSplat's under quilt calculator here: https://www.hammockforums.net/forum/...=1#post1317305 This file contain's the original work sheet, plus my modified version, so you can choose which works best for you.

Also, to help prevent down shifting, you may consider creating more, narrower channels.

**rstetz** · 05-19-2015, 10:27

Appreciate the help!! What would you recommend putting the channel width at then? 7 inches? We were just trying to use a number divisible by 56 to make it easy for measuring so we were deciding between 7 channels at 8" or 8 channels at 7" and chose seven 8" channels to save sewing time. The spreadsheet recommends 7.697" width per baffle, that's really not that much of a difference from what we have so I'm assuming it's not that huge of a deal? (then again, i'm not the expert ha)

**MAD777** · 05-19-2015, 11:45

How thick do you want your UQ to be? Thinner UQ's require more baffles than thicker ones.

**rstetz** · 05-19-2015, 13:29

2-3" would be nice...something to keep warm in 40-30 degrees

**-c0de-** · 05-19-2015, 15:33

Originally Posted by Boston

This is known as a differential cut. The reason this is done is to avoid compressing the down when the under quilt is snug. It's pretty much necessary for an under quilt to work the way you expect. In the early days of hammocks people didn't do this, and had a lot of problems with quilt performance. No body i know of sells a quilt that doesn't have a differential between the shell layer's.

You can find my mod of CatSplat's under quilt calculator here: https://www.hammockforums.net/forum/...=1#post1317305 This file contain's the original work sheet, plus my modified version, so you can choose which works best for you.

Also, to help prevent down shifting, you may consider creating more, narrower channels.

Hey Boston,

Here's a dumb question... Would it be beneficial to also make sure a top quilt had a differential cut? You are essentially doing the same thing (pulling it tight against your body .vs. tight against a hammock).

**boulderv7** · 05-19-2015, 17:37

Originally Posted by -c0de-

Hey Boston,

Here's a dumb question... Would it be beneficial to also make sure a top quilt had a differential cut? You are essentially doing the same thing (pulling it tight against your body .vs. tight against a hammock).

Top quilt doesn't need a differential IMO. Its not typically compressed on you like an uq would be compressed by your weight. The down lofts over and around you. That being said, I think there is some benefit to it....just not enough to be worth my time to make one like that.

**Boston** · 05-19-2015, 19:57

A top quilt will benefit from a differential by preventing the shell from squeezing as it wraps around your body. Basically to maintain loft the outer shell needs enough material to maintain a larger radius, otherwise its pulled inward. This is most noticeable in the footbox region, but can have an effect wherever the quilt wraps your body. This is much easier to accomplish with longitudinal baffles vs lateral.

A wider quilt will compensate for this simply by having more material to "bunch up" and you wont notice as much. If you try to make a quilt that fits tght to your body you'll notice this effect much more. The only quilt on the market that I know of that uses a differential is the Renegade from Underground Quilts. That quilt is shaped to fit tighter.

**tinner58** · 05-20-2015, 09:06

Originally Posted by rstetz

Appreciate the help!! What would you recommend putting the channel width at then? 7 inches? We were just trying to use a number divisible by 56 to make it easy for measuring so we were deciding between 7 channels at 8" or 8 channels at 7" and chose seven 8" channels to save sewing time. The spreadsheet recommends 7.697" width per baffle, that's really not that much of a difference from what we have so I'm assuming it's not that huge of a deal? (then again, i'm not the expert ha)

I just finished a torso length UQ using CatSplat's calculator (thank you CatSplat for such a valuable tool). My main goal, after determining the size of quilt and baffle height, was to make sure that each chamber required 1 oz. of down. As of yet, I don't have a scale that I would trust to measure the correct amount. I was able to purchase my down from Wilderness Logics in 1 oz. bags. After determining the size and thickness of my quilt, I just played around with the number of chambers and percentage of overstuff to achieve the magic number of 1 oz. It worked extremely well for me and was quite happy with the outcome. Here is a picture of the quilt.
torso uq.jpg

**rstetz** · 05-20-2015, 10:19

Originally Posted by tinner58

I just finished a torso length UQ using CatSplat's calculator (thank you CatSplat for such a valuable tool). My main goal, after determining the size of quilt and baffle height, was to make sure that each chamber required 1 oz. of down. As of yet, I don't have a scale that I would trust to measure the correct amount. I was able to purchase my down from Wilderness Logics in 1 oz. bags. After determining the size and thickness of my quilt, I just played around with the number of chambers and percentage of overstuff to achieve the magic number of 1 oz. It worked extremely well for me and was quite happy with the outcome. Here is a picture of the quilt.
torso uq.jpg

Looks good! i'm assuming since you had the down in 1oz bags you just put the bag of down inside each channel and emptied? I unfortunately don't have that (at the moment) as I extracted the down from a comforter purchased on craigslist (which was a fun and messy task) so I just have 2 big garbage bags of down. I've read that using a shopvac's blower setting is the best but i don't have a shopvac that can blow so if anyone has ANY recommendations on getting the down into the channels, that would be great. I'm thinking buying sandwich bags and weighing out 1oz bags will prob be best and then dumping them in but let me know if there are any tips/tricks to this.