Not sure why this popped into my head, but once it did, started to think about it more seriously.
I like Climashield Apex material because of it's relative low cost, ease of use, it's warmth to weight ratio, and it's decent recovery and durability for a synthetic. I'm always thinking of ways to improve things cheaply though (the Scottish-Celtic blood?).
Apparently companies that make products geared toward the construction industry somewhat commonly make polypropylene based microfibers to put in concrete to improve it in different ways. Since they make this stuff in bulk and large quantities of it, it's relatively low cost.
Polypropylene microfibers are VERY warm. Remember the Thinsulate stuff, that was about 65% polypropylene (listed as olefin) and thin/small diameter, though i don't think they were originally technically microfibers, but that did happen later. The stuff is quite warm, but has some issues in comparison to down and other synthetics.
Since PP has lower thermal conductivity than polyester, 100% is going to warmer, depending on the relative fiber diameters.
One of the issues of using all, 100% loose PP microfibers though, is the issue of loft. This stuff becomes very densely packed without structure. Another issue is durability.
Perhaps a simple solution to increase the warmth of Apex at not much weight or cost, is to buy some of this made for construction PP microfibers and spread some on the top and bottom of a layer of Apex? Some would get into the Apex material, but some would stay on the surface of it too i would think.
Anybody ever try something like this?