The best way to stay warm and to keep your body temperature regulated on a hike is with the layering system. This may sound complex at first, but really is simple. The basics of the system are that you wear multiple layers of clothing that you can take off or add as needed. When you’re hiking and generating heat you remove layers to stay cool. When you stop for a break or camp for the night you add layers to stay warm. Below are the basics to know for each layer.
Inner Layer – This is the layer next to your skin. This layer is most often thermal underwear (top and bottom) that is designed to wick moisture away from your skin to keep you dry. If you are wet it is very difficult to stay warm. The best thermals are usually synthetic and are specially designed to pull moisture away from the skin to the outside of the thermal where it evaporates. Avoid cotton, as cotton doesn’t dry well or wick. A t-shirt can be included in this layer.
Mid Layer – This layer traps air and is the layer that keeps you warm. This can be fleece or any synthetic. Look for windproof fleece. You can add several layers to your core (chest) if needed. Be sure to bring something very warm to wear at night around camp. Any insulated tops or warm shirts can be added to this layer as needed as well as fleece pants.
For pants I like convertible pants that have removable legs so they turn into shorts. For hikes in areas that are cold in the morning and warm or hot later these convertible pants save you space in your pack and are easy to convert without removing your pants.
Outer Layer / Shell – The shell is the outer layers that protects you from wind and water (rain, snow). It must be breathable or your body will turn into a sauna. I know this because the rain gear I used in the Army was not much more than a rubber suit and when we wore it and the rain stopped the rain suits turned into sweat machines. A good rain top will have zippers under the armpits and other zippers to allow you to get fresh air when the rain slows.
Gloves – Keeping your hands warm and usable is essential to enjoying your hike. Remember that your gloves may get wet from cooking so consider a waterproof outer glove and a thinner inner glove liner. Again you can remove one or both of these as needed.
Headgear – A chunk of your body’s heat escapes through your head. By keeping your head warm you protect your body and increase your comfort. With layering you can adjust your head warmth as needed. A good hat to protect from sun and rain is an easy luxury, and a scarf for your neck protects from wind that finds its way around your clothing. I have a balaclava that covers my face for very cold conditions.
As you can see the name pretty much explains the system. There are many synthetic materials (and now improved wool even) to choose from. Any reputable outdoor shop can help you create an excellent layering setup for your hiking trips. You might even be surprised to find that you already have many of the items needed.