If you are an experienced hiker, you know that setting off without a mid-layer and wearing only a t-shirt is unwise and not recommended. In the past, the choice was fairly limited and people often pulled on a classic jumper or a warm cotton garment (not recommended). Today, there is an abundance of technical garments and it is not always easy to navigate the options! Here is an article to guide you through the various possible materials and help you with your next purchase.
We will classify these garments by insulating material, as that is the key property you should be looking for: the insulating material retains your body heat and prevents it from escaping to the outside. This is the most effective way to stay warm in a mid-layer garment. However, you should also pay attention to the breathability of this layer, as it must also efficiently wick moisture from your perspiration so that dampness does not build up against your body.
Materials used for a mid-layer garment
Fleeces
Fleece fibres, as they are known, are generally made from polyester, PET (polyethylene terephthalate) and/or other synthetic fibres (some are even occasionally made from recycled fibres).
The strengths of fleece fibres are:
• Highly breathable.
• Dries quickly — faster than synthetic fibres, wool or down.
• Insulates even when wet.
• Affordable price.
• Care and washing are fairly straightforward.
• Good resistance to abrasion and tearing.
The weaknesses are:
• A fairly average insulation-to-weight ratio: fleece is quite heavy compared to down, synthetic and wool.
• Low compressibility: bulkier than down and synthetic fibres.
Fleece fibres are used in garments that share the same name (fleece jackets, which are generally found with short pile but also long pile), as well as in softshell jackets (a type of flexible jacket that is both insulating, windproof and water-repellent: you can find more information by reading the article on softshell jackets). There are also fleece trousers, gloves and hats, and this fibre can also be used as a lining in certain garments.
Moreover, fleece garments are practical and often less expensive than garments using other insulating materials. That is why many hikers use them, whether for day hikes or multi-day trips — even if they are not the most technical and high-performance garments available.
Synthetic fibres
The vast majority of synthetic fibres are made largely from polyester and are often engineered to mimic the properties of natural down.
The strengths of synthetic fibres:
• Insulate well, even when damp.
• Dry fairly quickly, though still slower than fleeces.
• Less expensive than natural down.
• A fairly good insulation-to-weight ratio.
• More compressible than fleeces.
• Fairly easy care.
Weaknesses:
• Insulation-to-weight ratio inferior to down.
• Less compressible than down and bulkier.
• Less durable over time than down.
• Less breathable than fleece, down and wool.
Synthetic fibres are used mainly in padded jackets, gilets and insulated jackets. Synthetic-fibre padded jackets are generally less quilted than down jackets because synthetic fibres move less and stay better in place.
It is therefore a good choice for a relatively lightweight and insulating garment without paying the price of down, and for coping with perspiration and external moisture.
Down garments
Natural down is made from goose or duck feathers, with goose down generally considered to be of superior quality.
The strengths of down:
• Excellent insulation-to-weight ratio — very lightweight. Better than other insulating materials.
• Highly compressible and compact.
• Excellent durability.
Weaknesses:
• Poor insulation when wet.
• Dries fairly slowly.
• Higher price.
• Less breathable than fleece.
• Delicate care and washing.
• Some people may be allergic to it.
Down is used mainly in padded jacket-style garments. Down garments are heavily quilted to keep the down in place and prevent it from shifting and creating down-free zones with no proper insulation. This is why all natural down garments have that characteristic appearance of small adjacent tubes.
Down is an excellent insulator in dry conditions. Down garments are best used for rest or moderate effort to prevent perspiration from reducing their performance. You must also be confident they will not get wet — in which case they will insulate very little or not at all.
Down garments are therefore an excellent choice as a mid-layer to wear in the evening at a stopover, at a mountain hut or near the tent. They help keep the weight of your rucksack down and avoid the need to layer up with multiple fleeces, for example, in very cold conditions.
Hybrid garments
No single insulating material is perfect on its own, and each has weaknesses that make them fairly specialised but not very versatile across different uses. Over the past few years, however, manufacturers have developed hybrid fibres and fabrics combining several materials. The goal is straightforward: to combine the advantages of different products while eliminating their weaknesses — and to offer products with an attractive price-to-performance ratio for the consumer.
There are many types of hybrids:
• Down that has undergone a hydrophobic treatment to limit its main drawback — namely that it provides little or no insulation when wet. That said, it remains less effective than other materials.
• Garments made from synthetic down. The idea is to offer a high-performing product at a fair price. As warm as natural down, this type of synthetic down — such as Primaloft, for example — is very practical as it is highly compressible: it is the warmest and lightest synthetic insulation in the world.
• Fleeces made from wool and synthetic fibres to bring resilience and elasticity to the thermal comfort of wool.
• Windproof and water-repellent fleeces — the famous softshells. This is therefore a blend of a mid-layer and an outer layer. These make for highly versatile jackets, well suited to a wide range of activities, as they are often paired with a thin, flexible and water-repellent outer membrane that shields against most light drizzle and rain. This creates a versatile jacket and explains the success of softshell garments today.
It is certainly true that the perfect mid-layer garment or fibre does not exist (or not yet), but each has its qualities, which are worth knowing in order to make an informed choice based on your intended use and compatibility with the garments you already own. You now have the key parameters to assess the characteristics of garments you may be considering purchasing, and to kit yourself out properly for heading out hiking with peace of mind.
