fleece or polartec?

The hollow core fleece fibers appear to have the best CLO value as I recall from a long-ago thread. I dunno if they are still produced.

As a point of reference for hollow fleece fibers deer, elk and moose hair is hollow for more insulating value. I've seen a lot of deer beds in the Pensylvania woods where you could see the depressions made by the lying deer but no evidence of melting.

Just got my Patagucci Cap 4 hoody today, but haven't tested it in the field yet.

Theoretical wise, the answer will depend on a couple of factors. First, are you comparing them side by side independently or in combo with a windshirt or windjacket of some kind?

To get the full warmth of the Cap 4, you need a windshirt because it's so breathable.

Then you need to compare thickness of the fabrics. With the cap 4, it would be measured from the outside of the fuzzy square to the other side of the smooth part of the fabric. The stuff i just got isn't very thick.

But neither are most 100 wt and more "classic" type fleeces.

Re: weight, the Cap 4 is definitely lighter. I have a 100 wt Polartec AirCore fleece with 1/4 zip, no hood, and larger size which weighs more than the hoody, 1/3 zip, rather long sleeves with thumb hole, smaller/slimmer Cap 4 Patagucci garment.

In other words, the Cap 4 is definitely warmer per weight, provided a windshirt/jacket is used in combo.

But you have to think about other things besides warmth. The cap 4 will be more flexible and adaptable to a wider range of temps and conditions than will the more classic fleece. It will also dry faster. This is based both on logic and on the experiences of others reported here.

Regarding hollow-core fleece, afaik you can only find Polartec Hollow-core fleece with Lands End these days. Pure on the basis of CLO, such fleece is indeed warmer. However, it scores bad (even worse then regular fleece) on wind-resistance.

Regarding wind resistance, I consider wind resistance a moot point when combined with an outer shell. In fact that is one of the reasons I like fleece, it is highly breathable and allows you stay drier when active.

A light grid fleece combined with a windshirt allows for hiking in a wide range of conditions.
If you begin to overheat, unzip the windshirt and let the air flow through the fleece to cool you down and help keep you dry.

I personally do not want a windproof mid layer.

Of course I like a separate windlayer. I only wanted to say that you don't have to exspect any better windhandling compared with normal fleece.

Coincidentally, I have such an Aircore-fleece. Regarding warmth, the claimed 20 % seems only a marketing gimmik and I don't notice any real difference with regular fleece. And I doubt if there is a weightadvantage. My jacket (non LE full-zip) weights 18,6 oz. in size L, a Cap 4 hoody 8.5 oz. in size M.