I wanted lightweight insulation for my Hennessy Expedition Zip and I'm on a budget. So I kept fiddling around with different combinations of space blankets and polyfill insulation. With PuckerFactor's help I got a silnylon undercover made that doubles as a poncho. My aim was to clone a Hennessy SuperShelter, with the option of using the undercover for rain gear.
The poncho is silnylon and measures 59"x104". It has a slit for the head hole, much like the MLD ponchos, so it closes under tension. I didn't want a hood, so it has a 3" tall collar with a drawstring-- a gasket, so to speak. The hems are all used as channels and end in diagonals so they don't overlap. The bottom channels have 1/8" shock cord with toggles and a mitten hook, so they can be hung from the suspension and gathered. The side channels have 3/32" shock cord and toggles so they can be tensioned for the sides of the undercover. The finished undercover weighs 9.7oz with the stuff sack.
In my experimenting, I came up with using crumpled and folded space blankets inside a lightweight trash bag to use inside the undercover as insulation. Another forum member pointed out that Ray Garlington had come up with this idea a few years ago. See http://www.garlington.biz/Ray/Hammoc.../Insulator.htm for the Garlington Insulator web page.
The Garlington Insulator is simple, light and inexpensive, and it works. If you have an undercover, you can make the insulator in a few minutes-- just take a space blanket, crumple it, fold it to make several layers, put it in a light trash can liner, and close it with a rubber band. Put that between your hammock and under cover. Two will cover at least the same as a 2/3 UQ, if not more. I got about 2" loft on my first try. I added a space blanket on top of the two insulators for more layering and side protection. I was very pleased with the results. I did want more coverage.
I have worked in the electronics industry and came across large anti-static bags and I went to eBay to see what I could find. It occurred to me that I had already made a large mylar bag while experimenting with the space blanket and polyester batting. All it takes is a space blanket, folded in half, with double stick tape to make it into a bag. I wanted the light eight, the large size, and the reflective surface.
I bought the lightest, cheapest space blankets I could find-- Coghlans #8235 for $1.99 each. They are 52.5"x82.5" and weigh 1.6oz each. I used double stick tape left over from a Frost King window insulation kit. The double stick tape found in an office supply will work fine. I had some stick on Velcro dots to hook two pads together. It isn't necessary, but I had some anyway. I wanted lots of layers so I used one blanket for the bag, with two crumpled and folded inside the bag--- six bags for two 50"x40" insulators. About 10oz for the works.
Here's a folded bag with a strip of double-stick tape
Crumple the bag to get lots of surface area (looks like a Star Trek creature)
Stretch the blanket back out lightly and fold it in half, make another and stack them. I put a 1" piece of double stick in the middle of each side to stabilize the stack, coupling the top and bottom layer together-- I just pushed the middle layers out of the way.
Put the folded blankets inside the bag. I used five 1" pieces of double stick to hold the blankets to the bottom of the bag, just inside the tape line that will seal the final side. My idea was to help stabilize the layers inside. The insulator will be rolled up for travel and I expect the blankets to move around inside. They will need to be crumpled and fluffed up after storage.
The finished insulator. It will never be this smooth again!
The insulators in the undercover with the HH Explorer swung to the back.
A closer view
The under cover with the insulators and the rigged HH Explorer.
The coverage is good and can be shifted to suit while the sleeper is in the hammock. The tension on the undercover can be adjusted while in the hammock too--- you can reach the head end toggles on the shock cords.
And it is warm, with 2" or more loft plus the reflective qualities of the space blankets and the protection of the silnylon outer covering. You can lower the undercover a bit to get more air flow and reduce the reflected heat. I have concerns with condensation, but my previous experiments with space blankets and insulation showed no real problems. I'll reserve final judgment until I test in other conditions. Total weight for the insulators is 10oz and the under cover is 9.7oz , so the complete UC/UQ system is under 20oz.
You get a good poncho in the mix too. A similar 60"x104" commercial poncho is $60-$100. I did make a simple belt using light drawcord with a loop on one end and a mitten hook on a taut line hitch on the other end. The poncho is sized to cover my backpack and the belt holds the sides in windy weather. It rides just above my pack belt to keep it it place. The 59" width gives good arm coverage and the poncho covers to just below my knees front and back with a pack on. I wear a Tilley or OR rain hat instead of a hood.
The poncho used three yards of 60" wide silnylon, nine mini toggles, two mitten hooks, six yards of 3/32" shock cord, four yards of 1/8" shock cord, and a couple feet of 1/8" drawcord. The insulators used six Coghlans #8235 space blankets, a partial roll of double stick tape and five pairs of self-stick Velcro dots.
FYI, Coghlans makes a space blanket bivy/sack that is 36"x84 and about 3oz, model 9815. It has potential. AMK HeatSheet blankets are quieter and a little tougher. They would make better covers, but I think the Coghlans blankets crumple better.
Update: Somehow I balked at using light plastic, but it wouldn't be any moisture-prone than silnylon I think.
Stowing the insulators! I found that they need more venting than I imagined to roll them up for stowing and when unpacking them and fluffing them up for good loft. I took a paper punch and made 5 holes across each end. I was able to roll them up to Nalgene size with no major crunching. Regaining the loft was just grabbing the the inner layers and pulling them out gently, drawing air back into the bag and separating the layers inside. Secure them with a rubber band.