There are more options than ever before for lightweight winter insulation from water-repellent down through to Polartec's new Alpha synthetic that's designed to allow you to work hard without getting hot and sweaty.
To give you an idea of what's available, we've taken five different lightweight solutions from Arc'teryx, Berghaus, Mountain Equipment, Rab and The North Face and outlined what each is good at.
Check out the jackets by either scrolling down the page or jumping straight to your favourite brands using the links below.
Arc'teryx Cerium LT Jacket - £240 / 246g
New this autumn 2013, the Cerium LT is the lightest Arc'teryx down jacket in it four-strong range and it's a stunner. The ultra-thin rip-stop Nylon shell fabric is slightly translucent so you can see the down inside and the shoulders, cuffs and underarms along with the collar use the brand's Coreloft synthetic fill to cope with possible damp ingress.
The cut is sublime in a climber-friendly, fitted way that's also more efficient. But what you really need to know is that the 850+ super-lofting down means the Cerium LT is unexpectedly and impressively warm for its bulk and weight. No, it's not cheap, but if you want the best bang for your gramme in cold dry conditions, you won't go far wrong.
Initial impressions are that the Arc'teryx Cerium SL hits an elusive sweet spot between warmth, weight and bulk. There are lighter jackets out there, but they tend to be less warm. And warmer jackets, that aren't as light. Just right said Golidlocks.
Berghaus Furnace III Jacket - £170 / 332g
From this autumn 2013, all Berghaus down products use the brand's water-repellent Hydrodown, which means it doesn't turn into a soggy mess in contact with water, but instead keeps lofting albeit at reduced efficiency and will dry out faster and with less loft loss than normal down.
That said, it's still best not to get it wet, but if you do, it's not quite as disastrous as it would be with untreated down. The Furnace also inherits body-mapped zones at the side of the trunk from top-end Berghaus jackets meaning less under-arm bulk without functional loss of warmth.
Overally it's a decent all-rounder, the down is only 700 fill power so it's not as lofty as, say, the Arc'teryx CeriumLT, but it's still reasonably warm at the weight and the Hydrodown adds peace of mind. Reliable cold conditions packable warmth option with a medium fit.
Initial impressions are that it's a decent, all-round mountain insulation option with a bit of wet-weather tolerance if needed thanks to the Hydrodown. It's not super warm, but it's warm for the weight compared to fleece in particular and of course, the Pertex Microlight shell fabric is windproof, which ups warmth in breezy conditions.
Mountain Equipment Compressor Jacket - £140 / 370g
The super-versatile Compressor Jacket uses market-leading PrimaLoft insulation, zoned so there's a lighter grade 40g fill in the sleeves and side panels and a warmer 60g fill in the rest of the jacket. PrimaLoft is hydrophobic and works well even in damp conditions where down can be a damp squib.
It's not super warm, but it packs down well, has a reliable, no-nonsense design and a full helmet-hood which means it can double up as an ultra-light belay jacket as well as for more general lightweight hill use. It scores over down thanks to its knock-aboutability and damp weather tolerance and over fleece thanks to windproof shell fabrics, though it meets its match when things get sweaty.
As with other lightweight synthetic insulation, you get better water-resistance and robustness than with down thanks to the hydrophobic PrimaLoft fill, which retains loft better when wet, and score points over fleece alternatives thanks to better warmth to weight values and the windproof fabrics, which add warmth out in the real world. First impressions are positive.
Rab Strata Hoodie - £150 / 430g
Rab's new for autumn 2013 Strata uses Polartec's new 'alternative puffy insulation' which is claimed to be twice as breathable and 60% faster drying than market-leading competitors. That means you can use it on the move at output levels that would reduce you to a soggy mess in other insulated tops.
The downside is that it's not as warm as any of the other jackets here and the more breathable outer fabric isn't quite a as windproof either, but for warmth on the move in cold conditions, it's brilliant and also works decently layered under s shell as well. You could argue that it's not really puffy insulation at all, but it's easier to look at what it's good for instead, which is coping with hot and sweaty activity in the chill. If that's what you need, it's excellent.
So far we're dead impressed with Polartec's Alpha insulation precisely because it's not really like a traditional synthetic puffy insulation system at all. It's almost as warm and almost as weather resistant, but - and this is the crucial plus point - you can wear it on the move without boiling alive, something we're looking forward to this winter, when we reckon the simple, slim design of the Strata should be ideal from everything from cold weather mountain walking through to sub-zero biking. Simply brilliant.
The North Face Thermoball Jacket - £150 / 345g
The Thermoball jacket uses market-leading, wet conditions friendly PrimaLoft synthetic insulation but in a completely new form. The PrimaLoft Thernoball fill is in the form of tiny balls which, says TNF means it performs as well in warmth to weight terms as 600 fill weight down, but is better at handling knock-about use and getting wet when it will retain more loft.
The little balls aren't without their problems though: because they're balls, they roll about easily, so the lightweight 20D fabric has to be quilted to keep them in place, which reduces warmth slightly and ups weight just a little. It's also cut in a slightly boxy way, which won't suit all users. Having said that, it's definitely warm for a synthetic jacket of its weight - 335g in a medium - and not far off down.
We were skeptical at first, but the Thermoball technology really does seem to give down-like warmth to weight properties but with PrimaLoft's impressive indifference to water. Yes, it does cost as much as a similar down jacket and yes, hydrophobic down has narrowed the gap slightly but for reliably wet conditions we'd still always go synthetic and this is the best balance of synthetic warmth and weight we've used.
It is expensive and we'd prefer a less boxy cut, but if the fit works for you and your bank account can stand the strain, then this is a no-nonsense, cold and wet-friendly lightweight insulated top that you can use over or under other layers as you choose.