Can someone school me on the active insulation midlayers vs traditional grid fleece? I wear a Sitka core heavy weight zip t but it's getting a little worn out and a little tight for comfort. What are the big advantages of Evolve over grid fleece? Sorry if I missed this conversation somewhere in the thread already.
The comments made in response to your question are accurate.
The reason why we used both grid fleece and hybrid Primaloft Evolve with a face fabric is because the 2 fabrics - Evolve and grid fleece - behave differently. There is overlap in what they do, which is provide a little bit of insulation, but they both have compromises as well, which means that if we were to make the whole piece out of just one of them, it's basically going all in on the compromises, which we found through testing many variations that is not what provided the best performance in what we were looking for. In other words, it biases the piece to only have the benefits of either grid fleece or Primaloft Evolve. We found that makes the use case too narrow.
With grid fleece and Primaloft Evolve, there isn't just one "model". So we can't just say that one is more breathable than the other, or warmer than the other, etc. Some grid fleece is more breathable than others, and some is also warmer or less warm than others. Same thing applies to Evolve. There is more than one flavor.
Evolve, without a face fabric over it, is massively more breathable than pretty much any grid fleece. The problem with that is the use case is very narrow, and we found way too many environmental conditions that rendered it useless at doing its job - insulating. So we found through a lot of testing in the field, that we get the broadest range of use with Evolve by putting a very breathable face fabric over it. The face fabric blocks just enough wind to allow the Evolve insulation to actually insulate, but because the face fabric is so breathable it allows enough heat and moisture to evacuate so that we don't overheat. With active insulation pieces, breathability and wind resistance work against each other, and what we ended up with is a balance of breathability and a minimum viable wind resistance. What we call a hybrid configuration, is the combination of Evolve and the face fabric. This hybrid has a very high warmth to weight ratio compared to standard or grid fleece. So in areas that we need more warmth, but don't want to sacrifice much or any breathability, we use this hybrid.
Grid fleece, while it is an active insulation, has a much lower warmth to weight ration. But, it can have much better stretch, and it is much less bulky, while providing a little bit of warmth. We use it in certain areas to capitalize on those properties.
All of this being said, by targeting a balance that exploits as much benefit from grid fleece and Evolve into one piece, we found it provides a broad range of usability.