Q&D DIY Space Blanket Under Quilt

[DaleW]

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.

http://www.adventuremedicalkits.com/...p?product=146#

[Timberrr]

Interesting!
I like the simple design and low cost approach. I don't think you'll need to do yarn ties because the batting is all one piece which has nowhere to go.

A few questions:
How much UQ effectiveness do you think will come from the insulating qualities of the polyester batting (not much I suspect) and how much from the reflective qualities of the HeatSheet (a lot I'd bet)?
How will you attach this to your hammock and keep it from slipping out of place and keep it snugged up to your backside?

Thanks for sharing the project with everyone. I look forward to the results of your field tests!

[DaleW]

I have been developing a silnylon under cover clone of the Hennessy SuperShelter that is also a poncho. The under cover has shock cord in channels on all four sides. The end shock cords gather the ends if the undercover just like a hammock and the overage becomes the suspension for the undercover, which ties into the whoopie slings. The side shock cords draw the cover up close to the top of the hammock sides. The under cover keeps the under quilt up close to the bottom of the hammock.

If you wanted to use it more like a conventional UQ, I would go the AMK Thermo Bivy route and add some lines or shock cord.

It is very effective for insulation--- dead air space is dead air space. The whole idea of using filler is to keep the air from circulating and making convection currents inside the space. It also lifts the top layer of the fabric to maintain the space

I ran a test last night with two loose space blankets between the undercover and hammock and this version with the 1-1/2" of polyester is MUCH warmer. It is much warmer than a 5mm EVA foam pad too.

Condensation is a worry. The top space blanket should take the brunt and as long as i don't poke holes in it, the insulation will stay dry. I'm hoping that any accumulation of moisture is below the hammock fabric in the under cover "environment", leaving my backside and clothing warm and dry.

The other test is to see how it packs. I plan to put it in the hammock and roll the whole works up. That should protect it. It is fragile and that is where the Thermal Bivy would be better, as it is much stronger fabric.

You could sling something like this on the outside like a conventional UQ. A light fabric or net sling and some shock cord should pull it off. If you take it too far, you might as well build a regular UQ.
I could use light nylon seine twine to tie up a macramé net with something like a 4" grid to hold it up. That would be in keeping with the quick and dirty nature of this project. A net would be easy to use a slider-style suspension. You just want to cradle it enough to keep it close to the hammock.

[johnnyh88]

Really interesting and simple idea. I'd be concerned about tearing the space blanket too, but like you said, the emergency bivy might be more durable. How do you think a windshield screen (reflectix?) thing might do in comparison?

[DaleW]

I tried a windshield screen and I wasn't impressed. It might take the chill off a summer evening. My concoction has three times the loft and is 48"x60".

[psyculman]

Thanks for the post, many good ideas there.

Although not having the marketing glamor of 'adventure' rated insulations, off-the-shelf polyester batting is just as good as the expensive synthetic insulations for some items. Unless there is 'loft envy' .

[DaleW]

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.


Specs:

SpaceQuilt:

Materials: AMK Thermo Bivy (original model), 3 layers 4oz polyester batting
Loft: 1.5"
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

Size: 59"x104"
Weight: 9.7oz, with stuff sack
Packed size: ~one liter (Nalgene bottle)

[mrmike65]

Very nice! I like your line of thought on this. Since the primary function of the batting is to create dead air space, I wonder if there is any way to make an inflatible pad of a mylar-type material. I'm thinking something like two layers of mylar welded every 6" to create 2" diameter tubes. The tubes would run lengthwise with the hammock, allowing the pad to wrap underneath the body. slip that into a sleeve made of Driducks ponchos and I would think you would have the best of everything: heat reflectance, loft, weatherproofing, compactability.

[DaleW]

Very nice! I like your line of thought on this. Since the primary function of the batting is to create dead air space, I wonder if there is any way to make an inflatible pad of a mylar-type material. I'm thinking something like two layers of mylar welded every 6" to create 2" diameter tubes. The tubes would run lengthwise with the hammock, allowing the pad to wrap underneath the body. slip that into a sleeve made of Driducks ponchos and I would think you would have the best of everything: heat reflectance, loft, weatherproofing, compactability.

I tried an insulated air mattress and that worked too-- I didn't inflate it fully so it could flex a bit. They are much heavier than the space blanket with batting, or a space blanket "bag" with multiple layers of space bags folded inside.

I was thinking of just using a really cheap air mattress wrapped in a space blanket, but the space blanket "sandwich" will deliver as much effective insulation for less weight and expense.

Last night I tried a 2-person AMK HeatSheet with a 1/2" batt of some really light quilting-grade polyester fill. I was warm enough and making a bag from the 2 person HeatSheet is about like a 2/3 underquilt. I actually quilted it, using light braided seine twine for and an upholstery needle to make ties--- 3 on each side and one in the middle. The AMK is stretchy, so I think it will hold up ok. The HeatSheet material is very quiet too. It weighs 10oz and rolls up to about 5"x12" without wrestling it too much.

My under cover is silnylon, so I'm just asking to get condensation problems, but I have to note that the Hennessy SuperShelter is the same stuff. Hennessy uses an open cell foam pad for insulation and recommends using a space blanket on top, so we're right back to the same thing using space blanket insulators.

I did get some light condensation on the top of the space blanket insulator last night. I was using a Hennessy Expedition Zip, with a 32F mummy bag used as a quilt. The low was 56F and the humidity was 80%, and the dew point was at 56F too I think. Around 3 AM I could reach below and feel just the lightest hint of moisture. My clothing and the hammock fabric were not wet and I was quite comfortable.

You can lower an undercover a bit, making it more slack, and get a little ventilation that way. The trick with the space blanket is to get it close, but not quite touching the hammock bottom. The sides are okay for mild weather, but I would want something to help hold them up for colder stuff. I think stick-on Velcro dots would be a good experiment. I tried trussing one up with shock cord more like a conventional UQ, and it was too tight on the bottom and I think it is too much stress. Loosey-goosey with an under cover is the way to go.

I don't have high expectations on durability on any of the space blanket insulators. They are quick and dirty and should remain there. I think putting a lot of work into them isn't a good investment. If you got a year out of it I think you would be doing well. If the outer cover gets torn up, you could recycle it into the next one.

You could buy some very light nylon and sew up a quilted pad pretty quick and it would breathe too. I would couple that with a simple breathable nylon outer cover, which could be made by adding basic hems and gathering and whipping the top.

Or buy an inexpensive hammock on sale. The Grand Trunk Ultralight would make a good under cover-- maybe too breathable, but it would hold the insulation in place. The bare fabric on a GTUL is 9oz. I paid $15 for mine. That is ~$5 a yard and it is already sewn. Just take out the stock suspension and use 1/8" shock cord with toggles and a mitten hook for the UC suspension.

That's my $0.02 for tonight.

[darkknight0667]

This is very much along the lines I've been thinking for under insulation for my son's Yukon hammock. Glad to see that it works in concept. I'll need to get cracking on it.

Instead of the poly fiber batting, what do you think of using Insultex sheets? I would think that it would be lighter and even more compressible than the batting.