Q&D DIY Space Blanket Under Quilt
I made an underquilt today using a 2-person AMK HeatSheet and some polyester batting. I used double stick tape for tow sides and Velcro dots for the opening. I got a big roll of batting at Goodwill for $5 :) I'm using it in my SuperShelter under cover clone made from a silnylon poncho. I tried it this afternoon and it is warm-- I could feel it immediately. I'll be testing tonight. I do have concerns with condensation, but hopefully if it happens it will be below the main hammock fabric and it won't be a problem with the space blanket.
After getting it done, it dawned on me that the thing to use is an AMK Thermal Bivy. It is more expensive and heavier, but simple and more durable. I would add a few yarn ties through the bivy and batting with buttons for reinforcement. Rather than a fragile kludge job, this would be a very viable underquilt for use in any hammock with an accessory undercover and a 15 minute job to make.
SpaceQuilt overnight test
Two thumbs up! I spent the night in my concoction and it worked like a charm. I had a low of 52F and 86% humidity. I slept through the night without waking. There was a very light layer of condensation on the top space blanket at 7:00 AM-- no puddles or big drops. I was comfortably warm with no moisture in my clothing or the hammock body. I had a light polyfill quilt for topside insulation.
I think this will go to 40F. Using a 20F synthetic sleeping bag I would take it to 32F or a little lower with confidence.
My daughter popped in this morning and she helped me modify an original AMK Thermo Bivy. I had taken the seams out for another project, so we sewed shorted it to 72" and sewed up the foot end, removing the vent in the process. The side seam was simply sewn back approximately where it was. I put a triple layer of 4oz batting inside and used the stock Velcro tabs to close it up. With the waterproof fabric, I am reluctant to completely seal the perimeter--- if moisture does get in, it would be hard to get it dried out. This is a prototype too, so I want access to play with various fillers and layers. I will probably finish sewing the side, which has Velcro tabs halfway down the side.
It sits well in the under cover and it has enough body to it that I can move it around. With the undercover drawn up, it sits lightly against the bottom of the hammock and stays put. I felt the same reflected warmth that I did from the space blanket version. I may add shock cords to the ends like the Hennessy SuperShelter pad, simply whipping them to the corners and running them up to a mitten hook on the suspension. There is enough width for 3 season use, but I would go for the newer and wider AMK Thermo Bivy for colder weather. I would expect the weight to increase 6-8oz.
Materials: AMK Thermo Bivy (original model), 3 layers 4oz polyester batting
Outer perimeter: 32" wide by 72" long
Weight: 22 ounces
Compressed and packed size: 8"x17" (in a large silnylon roll-top bag)
Poncho Under Cover:
Materials: 1.3oz silnylon, 3/32" shock cord, 1/8" shock cord, toggles, mitten clips
Weight: 9.7oz, with stuff sack
Packed size: ~one liter (Nalgene bottle)