Synthetic Under Quilts, compression

[Snowball]

I was reading about Synthetic Under Quilts and the materials and then I remembered someone forgot about compression. It is not a project and the numbers are more or less fiction but the differences are true.

When we make things like a Synthetic Under Quilt we think in 2D flat (most do) but fact is its used in a 3D environment. It forms a curve around you (cross section) and likewise in the length. The important thing to remember if you compress the isolating material you also reduce the air and then you don’t get the full benefit of the material you are using. In other words you are dragging material you don’t benefit from. If all 3 layers have the same size you will compress the insulation. You have to offset the outer layer’s dimensions with the thickness of the insulating material. It is however not as simple as adding the thickness of the material to the length. If you look at the numbers on the pictures you can see what I am talking about.
Let’s say your insulation material is 1” and you compress it to ½” then you are dragging ½” of material (weight and bulk) for nothing. You are spending energy dragging it and maybe you could have reduced the cost by selecting a thinner version if it lives up to your expatiations/needs.

I made the drawing's to satisfy my own curiosity but by sharing I hope it can save someone from this pitfall.
3D.png Cross s..jpg Length diff.jpg

[MarkI]

Thankfully, the materials used are not stiff and can fold on itself.
Usually the inner layer will just bunch up some and the insulation will scrunch up a bit. It is more efficient for the inner layers to be cut a smaller, but it's much easier to not.

[WV]

That's precisely why the insulating layers of my hammocks, as well as the underquilts I make to supplement them are based on patterns made by measuring each side of the fifty or so triangles I draw on the underside of an occupied hammock - to accurately duplicate the curved surface so the insulation can be uniformly thick. I used to do it for each hammock, but now I've worked up a set of masonite pattern pieces that work for all my current bridge hammocks. There is a small irony there - it was essential to do this for gathered end hammocks, but bridge hammocks are much more forgiving when it comes to fitting underquilts. Still, it's worth it to me to get more insulation from a thinner (but uniform) layer. YMMV, HYOH, etc.