Many/most small PSK will include a mylar "space" blanket or a plastic sheet. I was wondering, if I needed to rig a sun shade to protect me from the rays of the summer sun while I rested during the heat of the day, would one material be preferable to the other?

Seems like the mylar would be the winner since it is not only opaque but also reflective, but maybe in actual use, there's little practical difference. Was wondering if anyone had any practical experience with this. I'm thinking of a worst case scenario like being in a semi-arid or desert region with no natural shade, like trees or geological features, so I would need to dig little trench, hopefully to find cooler ground, then put the sheet over the hole.

Thoughts?

We did tests in college in the desert of central washington.
Temps were close to 120 F.

The winner overall -- black plastic

The thicker laminated space blankets with the reinforcing threads came in 2nd.

The emergency blankets let a lot of light through (heat),
even with water sitting on top of the emergency blankets they were
hot.

You did have to be about 3 feet from the materials for air circulation or you would cook.

Of course.

Very interesting results. What exactly do you mean by "black plastic"? Do you mean something like thick, contractor-type black trash bag material?

And the "laminated space blanket" is the Space brand blanket--metallic on one side, red or blue plastic on the other side?

I'm rather surprised and disappointed that the basic mylar sheet performed so poorly in providing shade. Well, glad to learn something new about something I have been taking for granted.

I carry a couple of 3 mil contractor black plastic bag for sun shade however, I have never actually used it under field conditions. I also carry 8, eight inch cable ties and duct tape to make groments, etc. This set up was suggested by several arid/semi arid "survival experts" books or forums.

The mylar is a low performer becuase it's just a thin layer of reflective material on the plastic- hold it up to your eye on a sunny day and you can see through it.

Too bad the space blanket performed poorly. Along with black and white trash bags, when I hike in the summer I usually always carry a small unbrella specifically for sun shade. Hmmm, I might have to do some shade testing on my hike tomorrow.

After some "reflection" I'm not too surprised that the space blankets didn't perform well in the heat. After all, they are marketed to be used mainly in the cold. They may have been designed to allow sunlight through as this could provide an extra advantage in some cold weather situations.

I wonder how the AMK Heatsheet would perform as a sunshade? With the orange backing it would be interesting to see how it compares to the trashbag.

We used the sheets of plastic you get at the hardware store.
They were the heavier gauge. The thinner you go, the more heat
gets through.

They also make good solar stills.

The heavier space blankets were the one that were colored on one
side, red or camo or blue as you mentioned.

Thanks, Clearwater. I'm curious, would you mind describing this experiment you guys did a bit more. Was its intent specifically survival-related? And how were the materials rigged? On sticks like a flat tarp, like a lean-to, or simply covering a hole in the ground?

I don't have a space blanket handy at the moment, but I have one of those mylar bags that electronics are packaged in. Yup, you're right. Pointing it up at the sun, light does get through.

Thank goodness, I can still keep my mylar-lined hats around to keep the guys in the black helicopters from stealing my thoughts. Wait, maybe I've been wrong about it actually being good even for that purpose...

I'll put this part first and then repeat it. DO NOT use a space blanket for this, but it is an interesting fact.
Mylar filters are one of the few materials recommended for viewing solar eclipses. WARNING!! - The mylar used for solar viewing is a special version. Space blankets are NOT suitable for this. (Unless you like having your retinas burned...)
-phil

For solar stills, you'd want a light gauge, clear plastic. Thick black plastic would be the least effective.

They were set up lean to fashion with a hole underneath to record
temperature. There needed to be at least 3 feet from the thermometer or the heat absorbed by the plastic would radiate to
it. It was so hot that we had to wear boots with thick soles and
wool socks or your feet would burn from the ground.

The coolest places were natural shade spots, as they handn't been
heated up prior, and were the most opaque of all.

Yes, clear plastic makes a better solar still, but black works too.
A friend of mine traveling in the Outback of Australia would tie
black plastic garbage bags around vegetation to collect the water
that would cook out.

Clearwater, did you test multiple sheets? At some point, I'm sure it's overkill, but if one sheet of black plastic is good, it seems that two or three layers would be better?

I wonder if two sheets with an air gap would be better than a single sheet, or simply stacking two sheets together? Top sheet heats up and heats the air between the sheets. That pocket of hot air rises and drifts up and away by convection. Also, the inner sheet may help block the heat that gets through the top sheet. Anyway, just a theory.

In the US army survival manual it recommends what you describe. Double layering the tarp material for a desert shelter with an open space (about 12') in between the layers. Supposedly it can reduce internal temps by 20-30 degF. Haven't tried it yet but I see no reason why it wouldn't work.