What I did for my car kit is take a thick wool blanket and use it with a homemade Tyvek sleeping bag. The Tyvek bag is very small,light and cheap to build. And even though it isn't exactly bulletproof, it does hold up quite well.

Polyester fleece can melt and burn. Given their insulation value it is no wonder people have been known to back up to a fire and catch themselves on fire while being completely unaware of the problem. There is supposed to be a Nomex fleece available that doesn't. Wool chars but won't melt.

On the other hand polyester won't rot or get eaten by moths. If you are storing blankets long term in less than ideal conditions, like perhaps in an underground cache, especially in buggy Florida, there is a good chance your wool blankets end up with holes. Lost my favorite OD green Marine 'Wooli-pulli' to moths even though it was supposedly moth proof. Put it into a drawer in January and it was fine. Come next December it was shot.

Most poly blankets let the wind blow through. The average wool blanket is tighter. But the more expensive tighter woven poly fleece is almost as tight as your average wool and poly with a laminated wind barrier blocks wind better than any wool blanket.

Wool maintains some insulation value when wet but so does poly fleece. Wool holds about 30% of its weight in water and sometimes more. Even at the minimum value it takes a long time to dry. Poly, wrung dry and shook, holds less then 10% water and dries swiftly worn wet.

Wool tends to be expensive for quality but ex-military blankets of good quality can be pretty cheap. Fleece is cheap, used to be cheap fleece was pretty miserable stuff and quality was more expensive than wool, but prices have dropped. Now good quality fleece, tight, dense, high loft stuff that doesn't pill, is cheaper than even cheap wool. Laminated fleece are still pricey but but they should be coming down as they gain popularity.

Also wool is heavy, when it gets wet it is heavier still. Poly is relatively light and after you wring it out it stays light. Don't wring that wool or it will get pulled out of shape. I have a trapezoid shaped blanket at home because it wasn't laid out properly when it was drying.

Wool combines many rolls. Tightly woven it will shed a good amount of rain. Tight and dense it blocks wind pretty well. And, of course, it is pretty good insulation.

Poly fleece doesn't shed rain unless it is treated with a water repellent. Treated with a DWR it sheds rain well and it will even after a few washes. The looser weaves don't stop the wind. This can be an advantage.

Personally I have both wool blankets and poly blankets. Forced to pick only one I would go with the wool. But usually I pick fleece and include a lightweight nylon tarp that is a little bigger than the blanket because it gives me a lot of options. In moderate cold the fleece alone is great. Add rain and the tarp becomes a rain shelter and, perhaps, a ground cloth. In wind the tarp gets lowered on one edge and becomes a lean-to. Colder and windier I tighten up the tarp. If it gets warmer and it rains, like it does down here, the tarp works alone. If it gets a lot hotter the tarp keeps the sun off.

The kicker is that the fleece blanket, light nylon tarp, a few lengths of light line and a few stakes weigh less and are less bulky than the wool blanket. And even after being stored for a few years I can expect it to come out of storage without holes.

You mean Nomex Fleece like this?

I have a few pieces of Massif fleece and some of their long u/w too. Good stuff, pricey but good.

From my scale measurement, I put my arty blanket at a little over 3 lbs. at 78" x 57", it is about 2/3 the weight of my pendleton blanket, which is thicker but less area.

The wife has my first blanket, which is 48" x 60". It fits her as well as my arty blanket fits me.

No, I am not a spokesman, nor do I have any interest in the company. When I find something that satisfies my desire as well as this does, I will advocate it. I feel the same way about my Leatherman Wave, or my Busse Knives, or my cast iron cookware, or my Montana canvas wall tent, or any of my Browning A-Bolt stainless stalker rifles. With all such things, I feel I am getting at least what I am paying for, and maybe a bit more. Sometimes a good deal isn't just about spending the least.

I still love wool. My favorite clothing items have been wool, though there are synthetics/blends that get real close to the top of my list too.

Before I found this laminated fleece, I would carry wool blankets. Standard fleece is not what I would consider good for survival gear, unless it is combined with other foul weather gear. Laminated fleece is just such a different beast, once I found it, I just had to make it my go-to choice.

Slightly obese custom home builder drives up and hijacks another thread. . .

I have noticed several mentions of using TyVek to construct different items. I am sure some have seen that DuPont released a new version called Thermal Wrap. It is reflective silver on one side and has a tested R2 insulating value. It might behoove one to switch to this product for future use.

It works, but is somewhat more expensive.

Yea, that's the stuff Desperado.

Nomex fleece could be important if your exposed to fire, high-heat or arc-flash. I wonder how it compares in feel and warmth to poly fleece.

A good polyester fleece pullover goes for less than $20. A similar one from that supplier in Nomex goes for $139. Interesting is that poly fleece was going for around that fifteen or twenty years ago.

Art,
The Firelite Pullover is comparable to a fleece sweater, loose fitting, comfortable. The Flamestretch pullover is body hugging, didn't want that for my app.

Do these products have the Nomex itch? It wasn't like wool, just funky feeling?

"Nomex itch?" That I can't say. It feels fine to me. The long underwear "Hotjohns", feels like poly, no itch at all, wear it all day.