Mid-Layer (insulating layer)

Insulation

Insulation is provided by the air trapped between the fibres of cloth and between the layers of garments, so two light tops provide more insulation than one thick one.  You have the advantage that you can add or remove them to regulate your temperature more easily, depending on weather conditions or the amount of physical exertion.  Garments should be loose fitting to trap air between the layers, to provide insulation and to allow air to circulate in hot weather. 

Clothing loses most of its insulating qualities when wet, whether from rain or from perspiration, so it is essential to keep clothing as dry as possible.  This entails reducing sweating when working hard by opening or removing garments and covering normal clothing with waterproof over clothing.  It is better to use garments that cover arms, shoulders and legs to help prevent sunburn and as well as giving much greater protection from insect bites, cuts and scratches and abrasions.

Tops

Garments need to be lightweight and low bulk - heavy woolly jumpers are not suitable.  Insulating fibre-pile, fleecy garments in synthetic materials are probably the most effective in keeping you warm.  Fleeces which are available in many different weights  and styles provide insulation and good wicking, so they are ideal over a base layer when the weather is good or under a waterproof if wet.  

One combination for the time of year that you will be undertaking your expedition is a 200 weight fleece jacket with full front zip (for ventilation), plus two 100 weight fleece jumpers (one being part of your change of clothing or as an extra layer in an emergency.  Softshell insulates, wicks and is also windproof. 

 

Trousers

Jeans and corduroy trousers are not suitable as they are often cut too tight, become very heavy, and provide little protection when wet.  They also take a very long time to dry.  Trousers need to be loose fitting, lightweight and quick drying.  Polyester is often the material used.  Tracksuit bottoms can be very effective.