by Aardvark » Sat 22 Sep, 2018 1:49 pm
The qualities that make a thermal are : 1. the type of fabric. ie Silk, Wool or a synthetic (polypropylene, polyester or similar - a petro-chemical, essentially plastic. It's a monofilament fibre. That means it does not absorb or hold any moisture. The fibre that is.) Cotton on the other hand is porous and will absorb moisture. Wool will also hold up to 30% of its weight in moisture but it has a property called heat absorption. It can help generate heat.
2. the weave of the fabric needs to assist in the movement of the moisture to the exterior (wicking). This is a hydrophyllic process. Body heat will generate a gas initially. ie Water vapour. A gas has smaller molecules but as they cool they will bind together to form a liquid. This needs to appear on the exterior of the weave to allow evaporation or movement through the next layer of clothing.
The simple fact that the fabric will wick means what is against your skin is drier. When your skin is wet it will lose up to 240 times more body heat than when its dry.
This is why a thermal is traditionally a skin tight layer. If the fabric is convoluted over your skin then it doesn't maximise the movement of the water vapour.
A second layer needs to be a bit more accomodating. These days the choice of thermals is almost unlimited. Anything that is synthetic is arguably a thermal. Regular synthetic shirts can act a layer.
I have something like 100 thermals of many types and makes. Some are sold as thermals and are specifically a loose fitting type synthetic shirt.
Polypropylene or similar nylon like fabrics are generally the cheapest and a good start point for most people. They are the skin tight type usually and provide a degree of stretch. Silk tends to be the most expensive. They usually have the advantage of minimising body odour, drying fast and providing the best heat to weight ratio.
Wool is a good option for many but not necessarily cheap. Can be scratchy if not the finest merino wool. Perhaps not as durable if fine merino wool.
Ever on the search for a one ended stick.