100wt fleece vest or cap 2 baselayer?

hmmm, good question. Best answer might be, depends and in what context.

Also, assuming a windjacket in conjunction?

Perceived warmth might initially go to the Cap 2, but if the 100 wt fleece is thicker than Cap 2 (i don't remember exactly how thick Cap 2 is), it may be more warm per weight efficient once active for a little while, because it will keep your core warmer at slightly less weight.

If you keep your core warm enough, it helps to keep the rest of your body warmer. But there is always that perceived warmth, and some folks just can't get over having cold arms etc for a while.

But the other benefit of a fully zippered vest especially, in conjunction with a windjacket, it's easier/faster to dump more heat and moisture if you need to. Like, if you're slugging up a steep hill wearing a fully zippered vest, unless it was howling wind, i would keep open the windjacket, and unzipp most of the way, the vest. Then on straight aways or going downhill, close it all up tight.

Also, a slight compromise. Get some polypropylene "wrist overs" and use them in conjunction with a vest and windjacket. They are very light, and brushed/fleeced polypropylene is fairly warm for the weight for low loft fabrics/materials. It's easy to take them off and put them on as needed, even with a windjacket and pack on, and your lower arms/hands are one of the least stinky/oil producing parts of your body, so you won't have to worry as much about the stink to high heaven aspect of PP–like when it's near your pits, groin, etc areas.

Anyways, that's what i would do if wanted or needed some compromise.

If you quantify warmth as which will get me sweating first/worst while hiking uphill, the 100 wt wins easily (and in just about any other context I can imagine).

You're probably right. I don't own any Cap 2 stuff, and while i've seen and handled it in REI before, i'm fuzzy on the details.

Basically, when it comes to non lofted, but woven or knitted garments, the thicker the material, the more insulating it will tend to be all other things being similar or equal.

For DIY's. Save yourself some money, go to Joann Fabrics, use one of their fairly regular coupons, and buy some of their common polyester "pile" type fabric. With a coupon, you can get it for around 5 dollars a yard.

It's thicker than 100 wt fleece at a similar (maybe slightly less) weight. Make a vest out of it. Great stuff, combined with a good windjacket, it's basically "Alpha" type material but more ideally breathable. So breathable, especially in vest form that a zipper may not be needed.

It's similar to Polartec Thermal Pro stuff, but at a fraction of the price.

Only issue is that it's not as durable as regular Polartec fleece and likely slightly less durable than Thermal Pro stuff. (I wonder if sandwiching it between some nylon noseeum mesh might help with that?)