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  1. #1
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    Cool Multiple questions as I plan a synthetic underquilt project

    Hi! I'm going to purchase materials to make a synthetic underquilt (and top quilt too, but I don't have Q's about that). Currently I only have a Costco top quilt and underquilt so obviously that's quite limiting in terms of weather/time of year I can backpack (though with the faux baffles and the "clew" suspension I have taken the set down to about 38 degrees, though I admit I was NOT toasty warm). Anyway I need this underquilt to go down to, preferably, 25 to 30 degrees with its matching topquilt.

    So, here are the fixed pieces of information: My hammock is a standard gathered-end hammock that I sewed myself. The topquilt I'm going to sew will have a layer of 2.5-oz. Apex AND a layer of 3.6-oz. Apex for a total of 6.1 oz. of Apex. The underquilt will be a full-length underquilt (though I'm short and my hammock is only 9.5 feet). Both the topquilt and underquilt will be 1.1 oz. ripstop nylon (calendered) on the outside and .66 oz. membrane taffeta nylon on the inside. I'm a pretty average sleeper (neither warm nor cold). Lastly, I'm a relatively experienced sewist so I'm not afraid of a challenge.

    Here are the possible variables, a.k.a. my questions:
    1. If I use one layer of 2.5-oz. Apex and one layer of 3.6-oz. Apex (so, together, it's 6.1 oz. of Apex insulation), will the UQ be warm enough to go down to about 25 degrees?
    2. I'm very much considering a "clew" woven suspension, OR a wooki-style stretchy fabric suspension. So I wonder: what's the lightest-weight stretchy fabric that any of y'all have used for a wookie-type suspension? Could I actually use bugnet fabric?
    3. Should I cut darts in the side of the underquilt? (I'm thinking I want to do this to shape the UQ for more efficient warming.) If I use a clew or wooki-style suspension, will the darts then be counterproductive or cause any potential problems? Also: How many darts -- one per side in the center? Two per side?
    4. Similar to question #3 ... I'm also considering a knotty mod on the sides of the underquilt. So, with a clew or wooki-style suspension, will the knotty mod be stupid, useless or counterproductive? And, would having both darts on the sides AND a knotty mod be dumb or bad?
    5. I know that most DIY-ers don't like the way synthetic UQs look when they're hand-quilted to keep the insulation secure. (I'm talking about using acrylic yarn or a heavier thread to take small stitches, in rows across the whole underquilt, every 12 inches or so. These stitches theoretically hold the Apex in place so it does not shift, stretch or tear. I don't mind the way these stitches look, so I am considering using some.) So my question is: Without the quilting stitches, will the Apex stretch or tear -- or will the quilt lose some of its warmth? Other related question: If I tie the quilt stitches loosely so as not to compress the Apex, will cold air still travel through those quilt stitches?


    That's a lot! I've combed through these threads a hundred times and have found so many helpful pieces of information about DIY hammock gear (thank you all!) ... but I still have these questions. Any answers/info/opinions at all would be very appreciated.

    Thank you!
    I have sewn my own: Backpack, hammock, bugnet, tarp, "Costco" top quilt with faux baffles, and Costco underquilt with "clew" suspension.

  2. #2
    New Member
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    Apr 2012
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    I would take a look at the Simply Light Designs Trail Winder under quilt. It uses Apex insulation. A new version has the option of a second snap on layer of insulation using KAM snaps to give it two temperature ranges. It uses a knotty-mod at the center of each side.

    I have been thinking that the Apex could be glued to one or both of the fabric layers to avoid the need of quilting stitches. Wiggy's uses that concept in his sleeping bags and clothing. See his description of Lamilite. 3M makes some spray adhesives that would work: 45, 77, 90, and 98.

  3. #3
    New Member
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    Hmmmmm! Thank you -- I didn't know about the Trail Winder. I will look at it!

    And adhesive -- I hadn't considered that. The plot thickens ...

    Thank you for your thoughts.
    I have sewn my own: Backpack, hammock, bugnet, tarp, "Costco" top quilt with faux baffles, and Costco underquilt with "clew" suspension.

  4. #4
    Senior Member
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    Sep 2021
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    SW Wisconsin
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    Gold Armour 10.4
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    After making an underquilt following the basic RBTR instructions, with a couple of differences. I measured the inner layer to the dimensions I wanted it to be, and added 4.5" in width to the outer layer, and 2" to the length. This was to reduce the amount "squish" to the insulation by adding the slack on the outside.
    It was a pain in the neck getting the "pleats" even on each end when sewing it together, but it worked pretty well.
    You probably don't need darts in the insulation, it conforms very well. It's pretty solid once sewn together.
    I wouldn't worry about gluing the outer layers to the insulation. Once I got it done, it seems fine, and I don't see a need for it. I think it would take away from the feel, and make it harder to pack.
    You can buy 6oz apex from Dutch. It would save the hassle of stacking insulation, and probably reduce the price.
    Stacking your costco quilt and a synthetic quilt will probably get you down pretty far in temps, and extend your range. Shug has a good video on stacking quilts to stay warm.
    Good luck with the project!

  5. #5
    Senior Member WV's Avatar
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    I've modified a couple of flat rectangular down quilts to use as underquilts and also made some two-layer synthetic quilts, and I suggest using darts - two on each side and one at each end. With two layers of synthetic insulation you can sew one to the top layer and the other to the bottom, then put the darts in separately on the two layers before you join them at the edges all the way around. I'd experiment with the darts (and the end clews or stretch fabric suspension) by pinning just the top layer and trying it on the hammock. You could use spray adhesive (sparingly! Wrinkles in light fabrics that are glued closed are hell to get out.) Another way to keep the insulation from shifting is minimal sewn-through seams to the fabric layers. One longitudinal seam sewing the top layer, and two horizontal seams for the bottom layers, so the seam lines are offset. Dividing the bottom layer in thirds that way would even allow adding a third layer of insulation in the middle section, perhaps just sewn at the edges. Make the bottom layer bigger, with correspondingly bigger darts so the perimeter matches the top layer. Go for it! I'm looking forward to hearing what you decide about the suspension. On reflection, don't use spray adhesive on the first quilt. It's probably not needed. My modified down quilts have darts and bungee perimeter cords, so the "Knotty Mod" might be a good idea - and lighter than a full perimeter cord.

  6. #6
    Senior Member WV's Avatar
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    Lorazepam, how did the sizing of your bottom layer work? Was 2" added to the length enough?

  7. #7
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    Quote Originally Posted by lorazepam View Post
    I measured the inner layer to the dimensions I wanted it to be, and added 4.5" in width to the outer layer, and 2" to the length. This was to reduce the amount "squish" to the insulation by adding the slack on the outside.
    I wasn't planning to do a differential cut (I think that's what you're describing?) but I will add it to the list of mods/methods I am considering. It seems less necessary in synthetic quilts (vs. down quilts with baffles, where it seems pretty important).

    Other things: The 2.5 and 3.6 layers of Apex are partly because RSBTR has those weights on sale right now. (Nearly all their Apex is on sale, but those weights are at a better percent off than other weights.) The other factor in layering the two weights of Apex is that there should be some (perhaps small) gain in warmth to layer the two -- because there will be air space between the two layers, and air space traps heat.

    And yes about adhesive probably making the quilt less packable -- good point, that makes sense.

    Thank you for sharing your experience with your quilt!
    I have sewn my own: Backpack, hammock, bugnet, tarp, "Costco" top quilt with faux baffles, and Costco underquilt with "clew" suspension.

  8. #8
    New Member
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    Quote Originally Posted by WV View Post
    Another way to keep the insulation from shifting is minimal sewn-through seams to the fabric layers. One longitudinal seam sewing the top layer, and two horizontal seams for the bottom layers, so the seam lines are offset.
    Okay this is an incredible idea. The two weights of Apex were mostly because of RSBTR's big sale on those two weights right now, but heck yes I should take advantage of having two weights and offset the quilting stitches or seams! And if I make those "quilt" stitches (by hand or by machine, not sure which yet) I can then more easily sew the darts and then sew the two layers together.

    Your post was full of excellent information and great ideas. Thank you!
    I have sewn my own: Backpack, hammock, bugnet, tarp, "Costco" top quilt with faux baffles, and Costco underquilt with "clew" suspension.

  9. #9
    Senior Member
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    Quote Originally Posted by WV View Post
    Lorazepam, how did the sizing of your bottom layer work? Was 2" added to the length enough?
    It seems to help, as there are no tight spots that I can see. The temps here have not risen to the rating of 30* for me to try it overnight. It has felt warm at 35 for a couple hours, but that is not the same as sleeping overnight.

  10. #10
    Senior Member WV's Avatar
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    Pixielauren, one more idea about two layers of insulation: if you have an air space between the insulation layers (generally not desirable because of the possibility of convective air currents, but better than having the bottom layer compress the top layer), you can fill that space with a couple of ounces of down. One of down's great advantages is that it lofts to fill available space, and this is one time when you want it to be able to move freely if there's room. I've made a number of hybrid insulated hammocks, combining down with a layer of synthetic insulation. The gap, if any, is at the low point, under your butt, so additional loft is welcome. The nice thing about this is that you can do it after making your two-layer synthetic quilt. You may not need to supplement the Climashield if you've sized your top and bottom well. A differential cut helps with synthetic insulation, too. (And part of what the darts are doing is making the top and bottom of the curved insulation layer different sizes.) Good luck. Avoid perfection. It's the enemy of the good.

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