Imagine a piece of 6 mil plastic, 10’ x 10’, pitched like a pup tent. Would it be hotter inside a black one or a clear one. For extra credit, how much would such a tarp weigh? I have been unable to find the weight per yard^2 online.
I am trying to find a substitute for my 8’x10’ woven poly tarp that is lighter, packs smaller and doesn’t cost much.
Thanks,
Rob
6 mil poly on the Home Depot web site weighs 57.4 lbs. for a roll 20 ft. x 100 ft. My math makes that 2.87 lbs. for a 10 ft. x 10 ft. piece.
I can only WAG at the first question, and since I’m the first responder and this is GQ, I’ll keep that to myself.
It’d depend on what’s inside the tarp, and what the tarps’ properties are in the thermal IR range. If the tarps’ properties are the same in the IR as in the visible (i.e., the clear one is also transparent to IR, and the black one is also absorbent in IR), and if what’s inside the clear one is also black, then they’ll be the same temperature. If what’s inside the clear one is more reflective, then it’ll be a bit cooler. But if the clear one is opaque to IR, and it’s dark inside, it’ll be hotter due to the greenhouse effect.
Will it be left in direct sunlight?
Not likely. I am using it to cover my hammock which will almost certainly be pitched under trees.
Rob
It sounds like something for nighttime use. If so the clear one should be warmer if near a maintained fire (or clear towards the fire, black on the ‘back end’), but you may lose a lot of heat to space with a clear one exposed to the stars. Unless you have a continuous fire or have high nighttime temps, a clear one may get dangerously cold under some conditions.
I don’t know for sure, but clear could be problematic.
Oh, I hadn’t realized it wasn’t going to be in the sunlight. In that case, the opaque one will be no cooler, and possibly warmer, than the clear one (again, depending on how they behave in the IR).
how is this going to be set up? draped over a rope between two tree? if so, why not try a couple of those shiney thermal blankets that fold up into a packet thats 4x4x2 inches or something close to that? or does the 6mil work better for you? not sure what sizes or costs are for them, but maybe its an alternative that would work
The clear is going to be hotter because it is see through, the sun goes directly through it, while the black tarp will reflect most of the sun light and also provide you with shade and the sun doesn’t come through! 
I suggest you take a look at tarpsplus.com I found my last tarp there a few years ago and I still have it and its going strong!
I’m no expert on light, but I’m pretty sure that if a black tarp reflected most sunlight it would be white. I think it’s black because it doesn’t reflect most of the light.
Wouldn’t being able to see through the clear one make it the (sorry) clear choice, even if the black one were a little warmer?
If you don’t care about seeing, then the “space blankets” that guestchaz mentioned would be a better choice than black.
If it’s an open ended tent it may not make much difference. For polyethlene sheet the black will absorb more infrared and conduct that to the interior as heat. The clear will tend to reflect a lot of the infrared away, and infrared in the interior can pass back out through the clear.
If you were trying to get the hottest tent you’d want an enclosed structure with a clear wall carefully angled to catch the most sun, and a black floor and wall on the opposite side to get a greenhouse effect going.
If you’re looking for the coolest tent, use space blankets to reflect the maximum amount of light, and leave plenty of air circulation also.