5 minute project: Add a thermal barrier to your tarp

Tarps are great pieces of shelter kit, typically being lighter and more versatile than a tent. We cover a few easy and useful methods in The Fieldcraft Course and students get very creative at coming up with ways to make them work for them. As versatile as they are, I never quit trying to come up with more uses for the pounds I carry. There’s typically a trade off between durability and weight with tarps, and I prefer to carry a little extra weight to ensure I have a good shelter.

I’ve always been intrigued by the reflective survival blankets like the Grabber and Arcturus types. For those unfamiliar with them, they are the relatively inexpensive emergency blankets that you can get for around $20. They typically have a colored side and a silver reflective side. This reflective side is very efficient at reflecting heat. You can use these in the cold to reflect your own body heat or that of a fire, or you can use it in the summer to reflect the heat from the sun to stay cooler. You can also use it to further camouflage yourself by hiding your thermal signature.

The problem with these is that even the “better” ones are still pretty flimsy for use as a dedicated shelter. This is because they are meant as emergency items, designed to keep you warm in an emergency situation. After a night or two out the stitching and grommets begin to fail, forcing the owner to resort to copious amounts of Gorilla tape to repair it. I’ve done this on a Grabber blanket I’ve used and abused far beyond what it was intended to do, and it does work. I double layer the tape where the grommets are, poke a hole through the material, and run a loop of bank line through and tie it in a Lark’s Head.

The other problem is that they are usually made of a very shiny material on the colored side, not very conducive to maintaining a low profile. Even though you can get some of these in camouflage or earth tone colors, they are still very shiny. Spray paint can help temporarily, but in my experience it doesn’t adhere well and typically leaves flakes of dried paint everywhere.

On the flip side, you can get a very high quality and durable tarp in any color and material you can think of. These of course rarely have any dedicated reflective properties on the underside for heat reflection. Wouldn’t it be nice to have the best of both worlds?

Actually, you can, and pretty easily too. You can use any tarp you want, no need to buy someone’s fancy thermal tarp. With this method you’ll be able to convert any tarp you want into a thermal tarp.

In this article I’m using my surplus USMC MARPAT tarp and the earlier referenced Grabber space blanket that I’ve doctored. You’ll want to get a space blanket about 1’ shorter in width and length than your tarp. You’ll also need about 20’ of 550 cord, about 12’ #36 bank line, 8 toggles, and some 2” Gorilla tape.

To start out with, reinforce the grommets with some Gorilla tape on your space blanket, and attach some small loops (2-3”) of bank line to each. If there are no center grommets on your space blanket just tape each side and poke a hole through.

Next lay your tarp out flat and lightly stake it out flat. Then lay your space blanket on top and get it close to centered up.

Next you’re going to get two measurements: one from the corner grommets on the space blanket to their associated corner grommets on the tarp, and another measurement for the side grommets. Add about four inches to these measurements then go cut a piece of 550 cord for each. Melt the ends and tie an overhand knot on each end.

Measuring for corner guy, Orange cord is my measurement piece

At this point you should have 8 pieces of 550 cord- 4 corner pieces and 4 side pieces. Next cut 8 pieces of bank line about 16” long each. Melt the ends on these.

If you’ve been to The Fieldcraft Course you’ll feel right at home with this next part. We’re going to make Prusik Loops with these. Start by connecting the ends of each piece with a fisherman’s knot.

Beginning of Fisherman’s Knot

Next attach each of these to the 550 cord pieces you made earlier. Lay your loop behind the 550 cord with the fisherman’s knot at the 10 o’ clock position. Wrap the upper half of the loop through the lower half three times, then dress it down. As you are dressing the knot, pull majority of the slack from one side, this will help make sure your knot ends up on the sides instead of the center of the loop where the strain will be. This is not really that important in this application, but practice makes perfect.

Starting of Prusik loop, do this two more times then tighten

Make sure that the Fisherman’s knot does not end up in the knot you’re making around the 550 cord. When you are finished it should look like mine. Three wraps working from the center out, with a locking bar across the front, knot on the side.

The Prusik loop is great because it can be slid using pressure on the side of the knot, yet when strain is placed on the loop it won’t slide.

Once you have all your Prusik’s attached, take the 550 cord piece and attach it to the small loops of bank line on the space blanket using another Lark’s Head knot. Pull all the slack though so the knot on the end of your 550 locks against the Lark’s Head.

Completed space blanket guy line

Next, take 3 or 4 pieces of Gorilla tape and reinforce the center of your space blanket as I’ve done. Do this on both sides of the space blanket.

You’re now done modifying the space blanket, so let’s get it attached. Set up your tarp, mine is set up Basha Style in the pictures. After your tarp is set up, spread your space blanket underneath with the shiny side pointing the way you want it to. To trap heat under the tarp, Silver side should be down. To reflect heat, Silver side is up.

Ensure all the Prusiks on your space blanket are slid out to the end of the 550 cord. Start at a corner and insert your space blanket Prusik through the grommet in your tarp, then insert a toggle. While holding the Prusik, pull some 550 cord through it about half ways.

Attaching first corner guy
A premade toggle from a plastic coat hanger I liberated from the Mrs.
Toggles can be made off the landscape too

Go to the opposite corner and repeat the process, except this time only pull the 550 cord until the slack in the space blanket is almost gone. We don’t want this very tight since we don’t want to damage the space blanket.

Tightened guy

Repeat this process for the other two corners, then the sides. If your tarp begins to bunch near the toggles it’s because you are pulling on the space blanket too much, just release some tension. If you’re using Bivy Poles like I did, I just looped the Prusik over the Bivy Pole point instead of using a toggle. Finally you can add a blunt stick or another Bivy pole to the center where you added the tape reinforcement to prop up the shelter a bit more.

Notice bunching of tarp, this corner is too tight

That’s really all there is to it. I set this up the other day when it was 100 degrees out, and with the shiny side facing out it was about 20 degrees cooler under my shelter. It felt really good with the breeze that was blowing through the elevated sides. That evening I had planned to take it down, but we had a thunderstorm blow in with about 40 MPH winds so I left it up. What better way to test the system? The next morning it was still standing, no worse for wear.

Completed installation

3 comments

  1. This is Good Info.

    BR- Thanks Clay, I edited your comment for security reasons. Feel free to email me at shocktroop0351@tutanota.com

    I also sent you an email as well, let me know if you got it.

    On Mon, Jun 7, 2021, 1:21 PM Badlands Fieldcraft wrote:

    > Badlands Rifleman posted: ” Tarps are great pieces of shelter kit, > typically being lighter and more versatile than a tent. We cover a few easy > and useful methods in The Fieldcraft Course and students get very creative > at coming up with ways to make them work for them. As versatile ” >

    Like

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