"I did try it over just a base layer at -20, it was fine but you could notice areas where your body shape compress the down slightly – over the shoulders for instance – where it felt colder. This is a slightly silly experiment but one that does show up cold patches in jackets. The Fjörm does not really have them, I suspect mainly because of its box wall construction."
Fair point - I can see that it sort of doesn't make sense! What I meant was that you do notice where and when you compress the insulation, it does feel a bit colder, but to really notice that you have to not be wearing mid-layers underneath and it needs to be minus stupid degrees outside! By "cold spots" I meant that with stitch-through jackets (in cross section, think a series of circles sitting on top of each other) you get distinct cold spots between those channels. But the Fjörm is a box-wall (in cross section; a series of squares sat on top of each other) so you don't get that.
My DAS parka is 11 or 12 years old I think - so they will have changed them since, but the Fjörm is a more wearable-for-things-beyond-belaying design than my DAS. The DAS is also heavier and bulkier despite being simpler. Probably about similar in warmth. Hood better on the Fjörm.
The Fjörm is a nicer jacket generally, but the DAS might be the better belay jacket just because it it synthetic.
Just wondering do you (or anyone else for that matter) have an opinion on using synthetic fill in certain areas of the jacket?
Is it likely to last as long as the down or collapse before the useable life of the jacket is up? Or is that whole synthetic insulation collapsing thing a legacy from an earlier generation of materials?
I know you mention that you are using a 10 year old DAS. Has there been any noticable degradation of the synth insulation? It will be difficult to gauge I imagine as any changes will be gradual and not sudden.
Good question Ronan. I've had my DAS so long I can't really remember what it was like when young, but I don't think it has degraded particularly significantly. I don't know what insulation is in there though, it might be a pre-Primaloft one.
I definitely remember seeing friends synth sleeping bags in the 90s noticeably collapse over a number of years, but perhaps modern synthetics are better?
With the Fjörm specifically the synthetic bits are rather small so I can't imagine it being a big issue, of course though I have only had it 6 months or so, so you wouldn't expect any thing noticeable in this time.
It is a good point though as there seem to be more and more mix synthetic and down jackets around, but one plus point for all down jackets has always been how well they last. My TNF Nuptse, bought in Dec 1995 still works fine and will be 20 soon-ish!