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Base Camp
While an awful lot of time and effort goes into choosing outer shells and mid layers, much less thought is given to the clothing worn beneath them. Yet ironically, no amount of breathability or waterproofing is going to keep someone comfortable if the layer next to their skin is cold, wet and clammy.
It's odd really; most people can get their head around how their top-end, £300 jacket keeps rain out yet still ‘breathes' and it's elementary stuff to get a handle on how a fleece can keep you warm. But get the average group of walkers to strip off these two layers, and the odds are that they've got a cotton t-shirt underneath.
What an opportunity! First, for them to increase their comfort simply and relatively cheaply. Second, for the outdoor retailer to gain new customers and make extra sales by demonstrating their expert knowledge on what is a relatively simple subject.
So what does a base layer actually do? And why is it so important?
First, think about the way a body reacts to exercise: it sweats. The science behind this shows that as the sweat evaporates away from the skin it cools the skin, therefore helping to regulate temperature.
The problem is, if the body produces a lot of sweat, as it does when exercising vigorously, but the sweat can't escape because it's beneath a jumble of clothing, then it stays put, in liquid form, making the micro-climate beneath those layers very wet.
This is where hi-tech shell fabric comes into play. These are charged with stopping the rain/snow/wind etc from getting in, while miraculously allowing water-vapour (the evaporated sweat) to escape.
Simple really. But the system is flawed if the clothing layer next to the skin traps the sweat and prevents it from vapourising in the first place - typical traits of a cotton t-shirt. Instead of escaping through the microscopic pores of the outer layer, the perspiration is now being held next to the skin, making the wearer warm and wet when he or she is exercising hard, but cold and wet the minute they stop.
The solution to this problem is simple: just ensure that the layer next to skin can transport moisture away from skin and out into the outer layers, where they can do their jobs. This is the role of the base layer.
So which base layers are best? The real answer to this is that any technical base layer is going to be better than a cotton t-shirt, but there are a few different fabrics out there, and they all do a slightly different job.
Firstly, the synthetics. These can be divided into Polyester, which is the most popular, and Polypropylene.
Polyester works by using different weaves on the outside and inside of the garment, therefore taking moisture off the skin and spreading it out. It is cheap and it's tough, but it can suffer with odour retention. Some manufacturers get around this by treating it with an anti-bacterial treatment. These tend to do the job when the garment's new but go off over time. Other, more expensive tops include silver oxide fibres within the fabric. This is effective and lasts, but it does add cost.
Polypropylene is quite different to polyester and works by being hydrophobic, meaning basically that it dislikes water so won't absorb it at all. This makes it very quick drying - perfect for those that really pour sweat - but against it, it tends to hold odours even more than polyester.
Both these synthetic fabrics rely on petrochemicals for production, so neither is particularly green, although some manufacturers are now using recycled fabrics and also producing garments designed to be recycled.
The other main option for a base layer is merino wool, which works differently again. The main thing here is that the wool actually absorbs the moisture, meaning it dries the skin very quickly. But unlike cotton, which then holds the moisture against the skin and feels cold, the wool then releases the moisture quickly so continues to feel comfortable and allows the outer layers to still do their job.
It has other advantages too. It is incredibly temperature tolerant, actually feeling warm in cold conditions and cool when the going gets hot; and it also resists odour, so is perfect for longer trips, such as multi-day hikes or treks. It is also a naturally occurring product so a little more environmentally friendly.
The big disadvantage is the price, with good quality merino tops typically costing twice as much as a synthetic one. It can also be quite fragile in comparison to the synthetic fabrics.
There are also polyester/polypropylene hybrids and synthetic/merino hybrids, which try to achieve the best of both worlds. Most of them succeed to some extent, although it seems to depend upon the exact mixes of the weaves, and the conditions.
So what about style and fit? These tend to be a little more personal, and within this category, it is also worth looking at the actual weight of the fabric.
Most fabrics come in varying weights: heavier for winter, lighter for summer and this does offer some advantages; but in the most basic of layering systems, it's probably best to let each layer do its own individual job, therefore the base layer transports moisture away from the skin, while the mid or insulation layers provide the warmth. Therefore a mid-weight fabric will probably do for year round wear.
Style-wise, crew necks are versatile - warm enough, with appropriate mid-layers, in winter, yet not too much for a summer day. And long sleeves are also versatile as they can be pulled up on warm days and left down in winter. They can also protect the arms from the sun in summer.
And fit-wise, snug is best for performance, basically the closer the fabric is to the skin the better job it's going to do. But not everybody has the physique required for figure-hugging lycra, so some looseness won't detract too much and may even feel a little cooler on a warm day.
So that's it. Well, not quite...
Before the customer leaves the shop, there's just one more thing: if he or she now realises the benefits of a technical base layer top, surely they aren't going to carry on wearing their M&S boxers or briefs? Good job there's plenty of choice in technical underwear too...
