The first synthetic fill jacket that I purchased was a Mountain Equipment Fitzroy Jacket around eight years ago. It was one hell of a thing, fit to burst with PrimaLoft insulation, and it lived in the bottom of my climbing pack only to be pulled out during cold, wet and windy winter climbing belay stances that you so frequently find up in the Highlands.
The bombproof, heavy and warm style of the Fitzroy was the trend when I bought my first synthetic jacket – it was built to last in the ‘ming’ that you’re so often blessed with in Scotland and it did the job extremely well. To be honest, synthetic insulation was the piece of equipment you purchased because you knew you had to, not because you wanted to – oh how things have changed with recent developments in synthetic fibres.
Synthetic insulation is made from polyester that has been spun into filaments that creates a pocket of air between each fibre. This pocket then warms up from your body temperature and thus, provides warmth. This is exactly the same way natural down can be used to keep you warm.
Down v Synthetic
We’ve not yet quite mastered a like-for-like synthetic alternative to down – it’s formation is just too unique – and so there are still some downsides (sorry) to synthetic insulation in comparison to it. That being said, there are also some upsides to using synthetic insulation over down.
Down offers the better warmth-to-weight ratio over synthetic insulation materials. Put simply, the unique 3D structure of down creates what is called loft which traps air more effectively than any synthetic fill in production at the moment. We could reach a point soon where synthetic insulation will be able to match up though. PrimaLoft is a good example of a type of fill that is getting very near to hitting that same warmth-to-weight ratio.
Wet weather performance
Down doesn’t have a natural ability to repel water (on a goose or duck it’s protected under larger, oily feathers), and so, if it gets wet it will clump together, lose its loft and in turn fail to trap warm air. Synthetic insulation on the other hand won’y collapse when it gets wet to the same extent as down, so in wet conditions you can still count on some insulation value. Bear in mind though, that these days it’s possible to treat down with a solution that gives it hydrophobic properties – so it’s hard to say outright that synthetics are better in wet weather than down! The debate rages on…
Plucking a helpless goose/duck of their lovely insulating down isn’t a very nice thing to do. Fortunately, many reputable outdoor brands these days (though not all of them) take measures to ensure that the down they use is responsibly sourced. This is an argument explored in our best down jackets test.
On the flip side, many are concerned about the impact of synthetic fibres on the environment – they’re normally made from plastic after all. To address this issue, brands like Polartec and PrimaLoft have managed to develop fills that can be recycled. There’s also a fully biodegradable and recycled fibre called PrimaLoft Bio which is due out soon. With these developments in mind, the scale is perhaps tipping in favour of synthetics on this front.
Give our Down and Synthetic Insulated Jacket Buyer’s Guide a read to get a real in depth look into the designs and technologies behind both fill types.
Best Synthetic Insulated Jackets
We’ve had a turbo warm February of 2019, which has stripped much of the crags of their ice and snow. This has made for interesting testing for the heavier-weight jackets in this roundup, but also perfect testing for the more ‘active’ insulation pieces. OM Editor Will has taken a range of jackets out with him in Snowdonia and the Brecon Beacons. I took a bunch up to the Highlands and the Alps during some ski touring weekends.