This week's Monday Tip is a spare clothing special for winter - what's best to carry in your pack as back-up insulation, conventional fleece or a down or synthetically filled jacket or something else?
Why Carry Spare Insulation?
Daft question? Maybe not. We'd always suggest carrying some back-up warmth in your pack as things get cooler, but you can use it in a few different ways. First, if you run warm when moving, but cool down fast during stops, you might want something you can throw on purely when you're stationary.
Next, if it's really cool or changeable, you might want extra insulation when you're actually moving - sometimes a hat can be enough, but when things get really gnarly, you may want to be able to wear your spare warmth on the move.
Finally, if you're caught out in an emergency bivi scenario, the spare warmth is there to keep you reasonably warm overnight, or at least alive.
Fleece has always been the traditional answer, but it has pros and cons. The pros are that it's relatively breathable and fast wicking and drying so it works well for active use under a shell adding warmth without reducing breathability - we find 100-weight, lightweight microfleece works best for this.
The down side is that adding fleece for stops may mean inconvenient stripping off of outer shell layers and the reverse when you start off again - a hassle - as fleece has little wind or water resistance. Plus warmer fleeces tend to be relatively bulky and sometimes heavy.
The modern alternative is some sort of synthetically-filled jacket using PrimaLoft or similar sandwiched in a lightweight shell. Warmth to weight ratios tend to be good, as does water resistance plus the shell fabrics make the garment windproof.
That makes them a great option for throwing over other kit if you stop for a quick break. Pull the jacket on over your other layers when you stop, pop it back in the pack when you move on. If it gets wet, it still retains reasonable insulation properties.
Where synthetic fills are less clever is on the move. Because there are two closely woven shell layers - inside and outside the insulation - breathability is seriously compromised and chances are, you'll get hot as soon as you start working hard.
The New Hybrids
So what's the answer? Well, a microfleece make sense if you're planning on using back-up insulation for active use, but a belay-type synthetically-filled jacket as a throw-on for use mostly when you're not moving.
But what if you do both? The latest answer are cunning zoned jacket which mix synthetic-filled panels over core areas like the torso and lower back, but have more breathable fleece panels elsewhere - Marmot, Rab, Patagonia and The North Face all have variations on the theme and on paper it does look like a good idea, but it's not been cold enough to find out how well it works in real life yet.
So for now, our advice would be to decide whether your spare warmth is likely to be worn for active use or not and choose accordingly - fleece on the move, filled belay-type jackets for mostly static use.