A flexible mid-layer can be one of the most useful pieces of kit in your expedition armoury. It should regulate your temperature, keeping you warm during periods of low activity but breathable enough to prevent you overheating as you ramp up the exercise. Additional qualities like wind and water resistance will help widen a reliable mid-layer to a dependable, year-round layering option.
In the following guide we will look at the different types of mid layers available and the important role these play in your layering system.
What is a mid layer and why are they important?
A mid layer is a garment typically worn as a second layer over a base layer for additional insulation in low temperatures. The term “mid layer” can actually encompass a range of quite different garments from fleeces, to soft shell or insulated jackets.
Each garment type will vary in terms of function, be that the level of insulation, breathability, or even mobility, and it is important to consider the conditions and activity you will be partaking in before deciding which type of mid layer is best for you.
Remember, the ultimate goal of a good mid layer is to keep you well insulated without causing you to overheat during periods of high activity. It’s also worth noting that, depending on the duration and nature of your outdoor activity, your mid layer is the one you are most likely to be regularly removing and putting back on, so there are stowability considerations to be had.
Which type of mid layer do I need?
Fleeces
Fleece fabric technology has come a long way in recent years, with today’s fleeces offering improved warmth, weight, durability and weatherproofing on their forebears.
Available in varying degrees of thickness, fleeces have historically been seen as the go-to for low temperature, low activity pursuits. However, that’s where ThruDark’s range of high performance fleeces stands apart from the rest. Utilising the latest in synthetic fleece fabric innovation from Polartec®, these are designed for high activity pursuits in the harshest of environments.
PHALANX
Take for example the Phalanx Fleece, making use of Polartec® High Loft™ fleece fabric. The patented high loft construction that gives the fabric its name helps trap more body warmth with the use of longer fleece yarns than conventional insulation. As an experience, the lengthened fleece yarns create a softer feel and provide maximum comfort when worn under an outer shell.
Most crucially though, HighLoft™ features a unique open mesh stitching pattern which helps vent excess heat during exercise. This will prevent you overheating and minimise the adverse effects that sweat build up has on not just user comfort but garment wear and tear.
MANTRA
On the other hand, the
As with the remainder of Polartec’s® synthetic fleece fabrics, Thermal Pro® provides excellent warmth to weight ratio plus the added advantage of anti-pilling technology. This means that whilst your fleece will perform even better than a pure wool alternative, it won’t look as tired with repeat use as we’ve come to expect from natural fleece fabrics.
.jpg?v=1727176478438&options=w_1296)
.jpg?v=1727176478438&options=w_900)
Soft Shells
Soft shell jackets are stretchy, mobile layers often constructed from a fleece fabric or brushed polyester. Their emphasis is on breathability and they are designed to offer a limited level of water and wind resistance. Typically speaking, you would opt for a soft shell layer instead of a fleece for more active pursuits that require mobility and durability such as climbing.
CENTURION
The jewel in ThruDark’s soft shell crown is our award winning Centurion Alpine Jacket. The Centurion makes use of three different Polartec® technologies to create a soft-shell optimised for climbing, abseiling, and all-round active pursuits in low temperature environments.
Each Polartec® fabric has been chosen specifically to maximise function. Polartec® Power Air™ makes up the main body of the Centurion in order to best target the body’s core. It features a revolutionary knit construction that encases fleece fibres within small chambers, rather than leaving them exposed on the fabric surface. This boosts warmth retention (as the chambers store heat more effectively) and minimises shedding by up to 5x with washing and wearing, which is better for the garment lifespan and better for the planet.
Power Air™ is also a dual layered fabric which reduces friction and minimises wear and tear making the Centurion a harder wearing layer than conventional soft-shells and fleeces. Polartec® Power Stretch™ is a performance-fit fabric used on the arms of the Centurion to allow greater range of movement when climbing or scrambling over adverse terrain. Another dual surface knit, this double structure allows Power Stretch™ to expand without compromising on durability. The entire Centurion is then bolstered with Polartec® HardFace™ technology, a patented polymer surface treatment applied to enhance durability.
.jpg?v=1727176513111&options=w_1296)
.jpg?v=1727176513111&options=w_900)
VELES
Following hot on its tail is our increasingly popular Veles Jacket. The Veles is a graphene-enhanced soft-shell jacket well suited for advanced technical pursuits owing to its light weight and versatile build. Designed to be compatible with a climbing harness, the Veles doubles up as a wind and water-resistant thermal regulating layer for hiking and trekking, and packs down well for multi-day expeditions.
The key to understanding the Veles soft shell is its graphene-enhanced construction. The strongest natural element on the planet, graphene is incredibly durable yet remains light and malleable, making it ideal for use in technical performance clothing. With Veles, graphene helps create a tough soft shell able to withstand the scrapes and abrasions of rock climbing or scrambling across challenging terrain.
However, strength isn’t its only benefit - graphene is also an excellent thermal conductor. It is able to effectively store heat generated by the body’s core and distribute this through the length and breadth of the Veles jacket to best manage your body temperature in changeable climates.
.jpg?v=1727176525465&options=w_1296)
.jpg?v=1727176525465&options=w_900)
Insulated Jackets
That’s right - you can wear an insulated jacket as a mid layer. Insulated jackets do not work by generating heat, but by trapping the heat generated by your body. Such a jacket will typically comprise of a water-resistant and/or rip-stop outer layer with insulation then stuffed within box compartments or “baffles” between the outer and inner layers. This insulation is usually made up of either “down” or “synthetic” fill. For further information on insulated jackets - check out our relevant guides below.
For the purposes of this guide, an insulated jacket may serve as a mid layer when worn beneath a waterproof hard shell. Layering beneath a waterproof hard shell will bolster the insulation provided by the jacket with a final weatherproof barrier, protecting you from wind and rain. This is just about the most robust layering system you can employ on a trip and is best exercised in situations of low activity and extreme, adverse environmental conditions.
ITHAX
For such a combination, your best bet is ThruDark’s
PrimaLoft’s® Cross Core™ series utilises aerogel for increased thermal performance. Originally developed by NASA for aeronautical use, silica aerogel is composed of more than 95% air and is the lightest solid material on the planet, making it one of the most effective insulating materials available for use. This aerogel is then moulded by PrimaLoft® into precision fibres that help insulate but at a low weight, ideal for a minimal feel insulated jacket that can slip easily beneath a waterproof hard shell for the ultimate weather protection.
.jpg?v=1727176503820&options=w_1296)
.jpg?v=1727176503820&options=w_900)
How should a mid layer fit?
As mentioned above, a mid layer is designed to enhance insulation and enable movement — therefore comfort is key, meaning fitment is crucial. Too loose and the mid layer will not trap heat as it should, too tight and this will reduce your range of movement.
Something we have also touched on is weight and stowability. The weight of a mid layer will range from bulkier and heavier fleeces and insulated jackets to lighter soft shell jackets. When choosing which is best for you, firstly consider the nature of activity and environmental conditions, but also the duration and nature of your expedition. Think about how much you need to carry and whether you can manage with the additional weight of a mid layer as and when this inevitably requires storing in your luggage.
And lastly, exactly why is breathability important? Profuse sweating is generally uncomfortable it can have an adverse effect on garment wear and tear. However, most importantly, sweating too greatly in a cold environment can cause your body temperature to drop too harshly, which can lead to complications such as hypothermia. That’s why adequate moisture management is vital for a number of reasons.
