What’s the warmest fleece material these days?

In response to James Penmans great question, on our Ask The Expert section:

Like most things in outdoor these days, the insulation or fleece layer is split between organic and synthetic products.

By far the most popular is synthetic fleece, which makes up a good 80% of the product used on the hill in the UK and further afield. Whilst most of the major brands have their own in house fleece mini brand (TKA from The North Face, for example), the market leader is Polartec. The main Polartec offering ranges in weight from 100 to 300, with the larger number being a thicker, more insulative garment. A Polartec 300 weight fleece will keep you nice and snug in all but the coldest of conditions. Click here to see a list of all our fleece, from lightweight summer fleece top to heavyweight winter hooded fleece jackets.

Other synthetic insulation layers can include heavier duty materials like Primaloft, which is also used in synthetic sleeping bags. Garments like The North Face Redpoint Jacket or the Mountain Equipment Fitzroy Jackets are great examples of this. They can be used over a base layer in mild to cold conditions or under a shell jacket when it gets really cold. One thing to look out for here, is the hood. Many of the better synthetic fill jackets have an insulated hood, but you need to ensure it will work with the hood on your shell jacket.

Finally, more Organic offerings using Merino wool are available. Icebreaker (a Webtogs favourite) make a 320 range of Merino Wool mid layers, the Rock Zip being a good example. Merino wool garments have a better warmth to weight ratio, so a 300 weight synthetic fleece will be thicker than an equivalent Merino wool garment offering the same insulative value. SmartWool are also in the mix for merino base layer and they make some really cleaver, warm and comfortable merino products, including socks and underwear.

On more of a technical side note, when it’s really cold, nothing beats down based products for cold (but dry) insulative value. Down’s primary method of keeping you warm is the loft effect, where the down separates and traps air, which in turn provides excellent insulation. It’s for this reason that down doesn’t actually work that well as a mid layer, as any layer on top will prevent the loft and hence hamper the insulating effect.

So, short answer, the warmest mid layer out there will be one of the synthetic fill jackets, closely followed by a good 300 weight fleece. When buying a fleece it is worth paying the extra for top fabrics like Polartec, they will last longer and are much more resistant to pilling, which is where the fleece bubbles into small knots, harming it’s integrity.

In our opinion if you were to start from the beginning then ideally you’d have a close fitting, long sleeve merino wool base layer then on top you’d put a mid to heavy weight Polartec fleece – you can choose between a 1/4 and full zip, the 1/4 will be warmer but the full zip is easier to take off or put on. The above the fleece a lightweight synthetic jacket like the Montane Fireball or a forth coming Polartec Alpha product. If it’s really cold (and dry) then add a down jacket to seal in that warmth and block out the wind.

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Choosing the Right Sleeping Bag!

When choosing a new sleeping bag it is very important to think about where and when you are going to use it.

The material the sleeping bag is made from, either synthetic wadding or down clusters plays a huge role in deciding the weight, warmth, size and protection that the bag offers.


These sleeping bags are much cheaper than down and can be washed and dried with greater ease leading to easier overall care of the bag.  If a synthetic bag gets wet it will still keep you warm as it will not lose as much insulation as a down bag would. Synthetic sleeping bags are bulkier and heavier than their down counterparts and cannot be compacted as much so they take up more space whilst not being used. They have lower warmth to weight ratio than down and the synthetic material tends to break down and lose its insulation properties faster than a down sleeping bag would. “Vango” make a range of synthetic sleeping bags that are lightweight and offer the ability to be compacted to a small size, these are ideal for backpackers who are limited on space but want a comfortable night sleep.


Down sleeping bags are very light and can be compacted into a very small space. They have incredibly high warmth to weight ratio and usually have a softer feel to them. Choosing down will incur a greater cost than choosing a synthetic bag and when choosing a down bag you should also look for a high goose down percentage, this can come at even higher cost. If a down bag gets wet it will lose insulation as the clusters will clump together and can provide less insulation than no sleeping bag at all! This can be rectified by a spin in a tumble drier and will restore the bag to its original state. Down bags are, however, more difficult to clean, you can’t just whack them in the washing machine. Ideally, you should get your down bag professionally cleaned by someone like WE Franklins of Sheffield (0114 268 6161) . If you do decide on a down bag then you must look at the “fill power”, this is a measure of how much space a set amount of down occupies in cubic inches and therefore how much insulation it will provide. The higher the fill power the better performance of the bag. “Mountain Equipment” makes a great range of high down ratio sleeping bags that have water resistant shells to keep snow and moisture out, these bags are perfect for extreme mountainous or sub zero adventurers.

In general if you are on a budget, allergic to down or will be using the bag in wet or damp conditions such as in a rainforest, caving or sailing then a synthetic bag would be the right choice for you. If you are going to be in extremely cold conditions, want very high warmth to weight ratio or want a durable and long lasting and compact bag then choose down.

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