Fleece or Synth?

Both the Atom SV and LT are standout pieces from Arcteryx but I find them hard to use during high aerobic activity like backpacking.

Despite the LT's increased breathability I have never backpacked in conditions where I was cold enough (even in winter) that I felt the LT was necessary. The problem is that the LT is too warm, and with the wind-resistant shell, not breathable enough. I sweat too much.

That said, amongst my friends there are a lot of fans of the LT for rock and ice climbing as it is capable of dumping excess heat while you climb but stay warm while you are standing still belaying. For light activity and mixed hard/light activity the LT is great.

I did use the SV for winter backpacking as a camp jacket, but as winter is concerned I now just head straight for even warmer jackets like the Das Parka and Fitzroy. I have never faced cold enough conditions (below 0F) that I've even considered using the SV as an active jacket.

Shelled synthetic like the LT and SV block the wind very well. Fleece does not. As a byproduct of blocking air movement, they also breathe less and are warmer.

Thanks Stephen, you are confirming my thoughts regarding active use. I can't even wear an R1 most of the time for what I do and the conditions I'm in, so I didn't think either the LT or SV would be used that way.

Does feel good for more relaxed walks or casual use, or for during breaks. Which I hardly take.
When I'm by myself, I need very little when active but I do get cold when stopping quick, so appreciate extra warmth. I can imagine using an Atom to layer over a down hoody, but not really looking for that use. My question is mostly about fleece vs Atom for relaxed/casual hikes in colder weather.

Casual, daily use exacerbates the already un-ideal loft degradation of synthetic puff. Go fleece. Big fleece.

Very good point. Also sums up what I want from this piece. Long lasting, low faff, cozy piece.

As other have said for active use I much rather fleece, but in saying that I use some of my old and beaten Syntehic clothing for knocking about.

i understand the mechanics and have experienced how repeated and prolonged compression of synthetic insulation has degraded it's loft/insulation quality over time, but am unsure why simply wearing a jacket would have the same effect. what's the mechanics of the degradation? i have an old patagonia synthetic parka that i've worn around town for years and haven’t noticed a reduction in its warmth.

If you compress certain areas like the back when sitting down, etc … Itll degrade with enough use

Simply wearing it is fine

With these UL insulated jackets, by the time youve degraded the insulation enough its probably time for a new one anyways as these UL shells wear out with hard use

Youll likely have a few holes and abraded spots

;)