Ilasco Explains

We’ve been working with outdoor clothing for over 30 years, and in that time have built up a collection of knowledge spanning everything from the basic outdoor terms to in-depth technical advice.
So we’ve started gathering that knowledge together and turning it into useful articles, so you can find the answers to all of your questions.

Looking for advice but don’t see anything here that covers it? Contact us and let us know – we’re working on new guides all the time!


It’s important to make sure you’re fully prepared before any trip outdoors; especially here in the UK where the weather can be very changeable, you might leave the house in sunshine only to be caught in a sudden downpour halfway through your trip.

The best way to make sure you’re ready for any situation is to make sure you’ve got a good layering system, but what is a good layering system?

What is a Layering System?

In the simplest terms, a layering system is using multiple items of clothing to keep you warm and dry, rather than one thick layer.
A standard layering system is made up of a base layer, mid layer and outer layer; although you can add additional layers or take them away as needed.

The way your clothing keeps you warm is by trapping a layer of warm air between you and it, which then acts as insulation.

When you have more than one layer on this creates multiple air layers which trap the warm air, this provides efficient insulation as when the air escapes from your innermost air layer it then gets trapped at the next one instead of escaping straight out.
If you were to just wear one layer (even if this was your biggest, thickest jacket) that one air gap can’t hold as much warm air, and doesn’t provide as much of a barrier to stop the warm air escaping.

Having multiple layers also means you have more control over your temperature. If you’ve only got one layer to wear, you’re more likely to find that you’re either too hot or too cold.
While if you have multiple layers, you can add or remove layers as needed to provide more or less warmth, windproofing or waterproofing as needed.

For example you may be planning a half days walk up a hill on a cool day, you’re wearing your wicking t-shirt and thermal jacket, your bag is packed and you’ve got your water bottle at the ready. You start your walk, but after a few hours the weather turns and suddenly it’s raining; if you’re following the rules of layering, you’ll have a waterproof jacket you can throw on to help keep dry, which you can take off again once it stops raining.

A base layer is the layer closest to your skin, commonly something like a t-shirt and long johns. The main job of a base layer is to move sweat away from your body (this is called wicking), if sweat is not wicked away from your skin you will very quickly become cold as soon as you stop moving or your level of exertion decreases. While rapid cooling may sound great when you’re imagining how hot you are after a run, not only can cooling so quickly cause illness, but imagine losing all that heat if you were up at the top of a mountain in the snow!

The most common fabrics for base layers are wool and synthetics (such as polyester or polypropylene). Which one you should choose will be down to personal preference, as each has its own benefits and drawbacks. Synthetics tend to be cheaper, are more durable and dry much faster, but are prone to retaining smell. Wool is more expensive and can be itchy, however it does not hold smell like synthetics and some people feel it insulates better.

Your decision could also be down to what you are using it for, wool base layers are not ideal for activities such as rock climbing or other rough activities as they abrade more easily than synthetic layers, but they could work well for hiking.

The only set rule for base layers is to avoid cotton at all costs. The problem with cotton is that it absorbs moisture and holds it, and when this happens it loses its ability to hold warmth. This will lead to you becoming cold and wet inside your jacket, regardless of the conditions you are out in.

The mid layer’s main job is to make sure you stay warm (it’s also known as the insulating layer), and is commonly a fleece or a thermal jacket (which can be filled with down or a synthetic down such as Primaloft).

Depending on the weather, you may find just wearing a base and mid layer is comfortable, with a waterproof stashed in your bag in case of sudden downpour.

A good mid layer will be able to keep you warm, but also be breathable to allow moisture to escape. Usually it wouldn’t be waterproof (you use your outer for that) but it is useful if they are water and wind resistant, to allow some protection when you aren’t wearing your full outer layer.

In cold weather you’ll need a thicker mid layer, and a thermal jacket may be the better option. While if the weather is warmer or you’re going to be doing some high-intensity activity, you should consider a thinner mid layer (like a micro fleece) that is likely to be more breathable.

The outer layer is your ultimate protection, and can be anything from a super-thin and lightweight windproof layer to a heavy and durable weather-proof tank-like jacket.

There can be a lot of differences between outer layer jackets, and the right one for you will depend on where you are going and what you will be doing. Before we tell you about the different types of jackets, we’ll give you a quick overview of some of the most common terms used to describe these jackets and what they mean.

  • Water/wind resistant
    • If a jacket is described as being resistant to water or wind, it means that the jacket will allow for some protection from water or wind, but if the weather is severe and/or prolonged you may find that you will still get wet and cold
  • Water/windproof
    • If a jacket is described as water/wind proof it means that the jacket offers complete protection up to a certain level. The level can vary depending on the jacket, but this can normally be found in the jacket description or from the manufacturer.
  • Breathable
    • If a jacket is breathable it means that it has some ability to move water away from the user. Depending on the jacket and fabric system this can be done in a variety of ways, but the basic idea is that it allows water vapour to move from the inside of the jacket to another area away from the skin, so you don’t feel damp or cold.
  • Softshell
    • If something is described as softshell it usually means it has a soft and stretchy outer fabric, for example a fleece or a pair of stretchy trousers or leggings. Just how soft and stretchy it is depends on the fabric.
  • Hardshell
    • If something is described as a hardshell it usually means the fabric has a smooth or plastic-y feel; and it will offer some degree of water protection.

And now that you know the basic terms, we can tell you about some of the main types of outer layers, and when you might use them.

  • Softshell
    • A softshell can come in a variety of weights, it generally has a soft/stretchy outer and more focus on breathability which make them ideal for active use with lots of mobility.
  • Hardshell
    • These jackets can be considered to be your classic outer layer, offering a variety of water and wind protection; and with the number of different fabrics available now there is a lot of choice on the market so you can find the perfect one for you.
  • Water/wind Resistant Jackets
    • Lightweight and offering minimum protection from water and wind, these jackets tend to be cheap and can be breathable. Although they don’t offer much protection they are ideal for keeping hidden in a bag just in case you need a bit of quick coverage until you can find shelter, or their breathability may make them ideal for use for activities such as running.
  • Water/windproof Non-breathable Jackets
    • Offering more protection from wind and rain, but without the breathability. These jackets come in a variety of weights, and can be ideal for either keeping in your bag for an emergency or for activities with limited movement (e.g. fishing, attending festivals or other outdoor events).
  • Water/windproof Breathable Jackets
    • These jackets can give the ultimate protection and can deal with a range of elements, but do tend to be heavier and more expensive than other options. If you’re planning a trip up a snowy mountain, you don’t want to be without one!
  • Insulated
    • An insulated jacket can provide a lot of warmth, but is usually only water/wind resistant. If you’re out on a chilly, dry day they are ideal; and are also great for layering underneath a waterproof shell.

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