If you are an experienced hiker, you know that heading out on a hiking trip with only a t-shirt and no mid-layer is unwise and inadvisable. 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 find your way through them. So here is an article to guide you through the various materials available and steer you towards your next purchase.
We will classify these garments by insulator type, as this 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. Nevertheless, you should pay close attention to the breathability of this layer, as it must also efficiently wick away moisture from perspiration so as not to trap humidity against the body.
Materials used for a mid-layer garment
Fleeces
Fleece fibres 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 damp.
• Accessible price point.
• 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 relative to down, synthetic insulation, 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 available with short or long pile), as well as in softshell jackets (a kind of flexible jacket that is both insulating, windproof, and water-repellent: you can find more information in 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.
Furthermore, fleece garments are practical and often less expensive than garments using other insulators. This is why many hikers rely on them, whether for day hikes or multi-day trips — even if they are not the most technical or high-performing option.
Synthetic fibres
The vast majority of synthetic fibres are made predominantly from polyester and are often engineered to mimic the properties of natural down.
Strengths of synthetic fibres:
• Insulate well, even when wet.
• Dry fairly quickly, though still slower than fleeces.
• Less expensive than natural down.
• Fairly good insulation-to-weight ratio.
• More compressible than fleeces.
• Fairly easy care.
Weaknesses:
• Insulation-to-weight ratio less favourable than down.
• Less compressible than down and bulkier.
• Less durable over time than down.
• Less breathable than fleece, down, and wool.
Synthetic fibres are used primarily in puffer jackets, gilets, and jackets. Synthetic fibre puffer jackets are generally less compartmentalised than down puffer jackets, as synthetic fibres shift less and stay in place better.
It is therefore a good choice for a relatively lightweight, insulating garment without paying the price of down, and for handling perspiration and external moisture.
Down
Natural down is made from goose or duck feathers, with goose down generally considered to be of superior quality.
Strengths of down:
• Excellent insulation-to-weight ratio — very lightweight. Better than other insulators.
• Highly compressible and takes up very little space.
• Excellent durability.
Weaknesses:
• Poor insulation when wet.
• Dries fairly slowly.
• Higher price point.
• Less breathable than fleece.
• Care and washing require delicate handling.
• Some people may be allergic to it.
Down is primarily used in puffer jacket-type garments. Down garments are highly compartmentalised to keep the down in place and prevent it from shifting and creating down-free zones — and therefore inadequate insulation. This is why all natural down garments have that characteristic quilted appearance of small adjoining tubes.
Down is an excellent insulator in dry conditions. Down garments are best suited to rest or moderate activity, to prevent perspiration from reducing their performance. You must also be certain they will not get wet — if they do, they will provide very little or no insulation at all.
Down garments are therefore an excellent choice as a mid-layer to put on in the evening at a stopover, in a mountain hut, or near the tent. They help keep the weight of your pack down and eliminate the need to layer up multiple fleeces, for instance, in very cold conditions.
Hybrids
Each type of insulator taken individually is imperfect and has its weaknesses, making them fairly specialised materials with limited versatility across different uses. Over the past few years, however, manufacturers have developed hybrid fibres and fabrics combining several fibres. The goal is straightforward: to combine the advantages of various materials while ironing out their weaknesses — and to deliver products in attractive value-for-money ranges for the consumer.
There are many types of hybrid:
• Down that has undergone a hydrophobic treatment to limit its main drawback — namely, that it insulates poorly or not at all when wet. That said, it remains less effective than other materials.
• Synthetic down garments. 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 highly practical thanks to its excellent packability: it is the warmest and lightest synthetic insulation in the world.
• Wool and synthetic fibre fleeces, combining resistance and stretch with the thermal comfort of wool.
• Windproof and water-repellent fleeces — the well-known softshells. They are therefore a blend of a mid-layer and an outer layer. These make for incredibly versatile jackets, well suited to a wide range of activities, as they are often combined with a thin, flexible, water-repellent outer membrane that provides protection against light drizzle and rain. This results in a highly versatile jacket and explains the popularity of softshell garments today.
It is clear that the perfect mid-layer garment or fibre does not exist (or not yet), but each has its strengths — and knowing them is key to making a sound choice based on intended use and compatibility with garments you already own. You now have the essential criteria to assess the characteristics of any garment you are considering buying, and to kit yourself out properly for heading into the mountains with peace of mind.
