# Thread: DIY 3/4 Underquilt differential question

1. ## DIY 3/4 Underquilt differential question

Hello, I have a few questions. 1. Approximately how many inches wider should the "bottom" she'll be vs the top to avoid compression? With approx 2.5-3 inch baffles.

2. Also should the length of top & bottom shells be different as well. It seems to me if the lengths are not the same then the baffles may need to be cut curved? Am I wrong? Curved baffles seem like it may add a challenge to construction.Any insight would be great.

2. Hey, just finished mine so I understand your questions. Not in a good spot to answer at the moment, but search for the Underquilt calculator. It will help a lot.

3. The width differential depends on the baffle height, max chamber height, and the # of chambers. Where w = finished width, d = differential width, r = arc length of each chamber, h = baffle height, and c = # of baffles: d = w + (r * c) + 2h

The length differential will generally be about inner shell length + double your baffle height. So if l = finished length, d = differential length, and h = baffle height: d = l + 2h

I definitely recommend using the UQ calculator. It takes care of all the math for you and tells you how much down you need etc.

For length differential, you don't have to cut your baffles with a radius, but it probably makes sewing a bit easier. I did square corners and it was a real pain to sew.

4. Give me a moment to find the thread with the calculator in it...

Here you go.

Hope it helps!

5. Here is an example of my DIY UQ with curved baffles, it may help.

My-first-UQ-shaped-baffles

6. Originally Posted by hangingclimber38
Hello, I have a few questions. 1. Approximately how many inches wider should the "bottom" she'll be vs the top to avoid compression? With approx 2.5-3 inch baffles.

2. Also should the length of top & bottom shells be different as well. It seems to me if the lengths are not the same then the baffles may need to be cut curved? Am I wrong? Curved baffles seem like it may add a challenge to construction.Any insight would be great.
1. For my 4 UQ's I have made, I have found at least an inch difference minimum per baffle chamber. If you use the UQ calculator mentioned above, adjust your max chamber height until you get numbers that are easy to measure and close to what you want.
2. I cut the bottom shell longer in length by the difference of the baffle height x2. So if you are using 3 inch baffles, I cut it 6 inches longer plus my seam allowance. These extra inches are sewed up the baffle ends, creating a bathtub shape to the bottom shell. This avoids compression of the down on either end. This measurement is included in the UQ calculator modified by Boston. Shaped baffles are not needed, IMO, but are cool but alot of extra work.

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