The Layering System - The Mid-layer

Millets 3 min readAdvice & Guides

In part one of this series we looked at baselayers and why they’re the best thing to wear next to the skin. Now comes the question of what to put on next. In part two we delve a little less deeply into the layering system and take a look at mid-layers.

Now I can say with a high degree of certainty that almost everyone reading this will own a mid-layer. The reason you may not be aware of this is because they are more commonly known as fleeces. 


There are no prizes for guessing what the principal function of the mid-layer is. It’s all about insulation. The fine loose fibres in fleece fabric trap air that in turn traps heat. Not really rocket science, but there is another often overlooked function the mid-layer performs.

You may recall the baselayer moves perspiration away from our skin, but where does it go next? Straight into your mid-layer that’s where. The mid-layer must not only be highly breathable to transmit moisture vapour, but must also be fast drying to deal with liquid moisture. It is for these reasons that cotton sweaters and woolly pullys just won’t cut the mustard as a mid-layer. In addition fleece mid-layers are also lighter and more compressible, couple this with prices starting at £10 or less you’d be bonkers to go without. If you want to take advantage of a £10 or less price tag take a look at the men’s Ullswater and women’s Grasmere fleeces by Peter Storm.


Apart from a few rare acceptations fleeces are made from 100% polyester, and differ little in thermal performance from brand to brand. So what do you get when you spend a little more? Higher quality fleece not only hold its shape better, but is also more resistant to bobbling and pilling which commonly blights cheaper high street versions. In particular keep an eye out for Polartec fleeces. Polartec are a specialist fabric manufacturer who makes some of the best fleece materials in the world.

The other important thing to understand is that fleece fabrics come in a range of different weights (or thicknesses). The most common weights available are 100 and 200. The number denotes the weight in grams of one square meter of fabric. 100 weight fleece is usually used in light-weight pullover fleeces and is designed for more active use or milder conditions. In contrast 200 weight fleece is normally used in full zip fleece jackets and is designed for less active pursuits or colder conditions.


Where fleeces are concerned there are a couple of features that are well worth understanding. The first of these, and one that has become much more common in recent years, is stretch. Stretch fleece greatly improves freedom of movement and comfort, however this is only part of the story. The really big wins come in thermal efficiency and moisture transmission. Close fitting insulation eliminates large air gaps which heat can escape through. In addition, when fleece is in better contact with your baselayer it rapidly absorbs liquid perspiration and moves it away from the body. For serious enthusiasts, stretch fleeces are now becoming the rule rather than the exception.

The final big benefit fleeces can provide is wind resistance. The UK is a windy little island but fortunately it’s not always raining. In these situations an outer-layer would be unnecessary, apart from the fact that traditional fleece offers little wind protection. It’s for this reason many brands offer windproof models. A classics of this category is the mighty Choktio II GTX by Berghaus. Berghaus use Gore Windstopper fabric to give you 100% wind-proof performance. In addition, some manufactures have developed their own windproof fleece fabrics allowing them to deliver options at incredible prices like the Windproof Fleece Jacket by Peter Storm.   


Check out our outer layer blog to finish of our three part series on the layering system.



Millets Author

Join the discussion