The most obvious reduction in performance comes because the water repellency of the outer fabric is lost, because of dirt, abrasion, water pressure or contamination with water softeners. This causes the fabrics to become saturated and the inside is likely to reach the dew point, causing condensation and a loss of breathability.

Conventional membrane waterproofs may also be punctured, membranes can crack, abrade and delaminate and seam tape can peel off.

Some of these problems only manifest themselves in extremely wet weather and the ShellTA gives you another tool to reinforce your waterproofs in those rare extremely wet conditions. It provides a “defence in depth”.

When you wear the ShellTA under your sack, ease the front fabric out from beneath your hip belt and shoulder straps to separate it from under layers.

The fabric of my sleeve was wet before getting in the ShellTA

When you wear it over a wet waterproof the water tends to stick to the ShellTA, providing a useful drying effect. Once it is saturated this effect diminishes and air circulation beneath the waterproof canopy is the only way drying will continue.

Although the ShellTA is made from a thin waterproof fabric, with little inherent insulation, two people sat together inside can share a surprising amount of heat that would otherwise be lost to the atmosphere. It’s also a very simple way of adding extra protection for your legs, without the hassle of overtrousers …and it doesn’t need to spoil the view: each person can open their side vent to peer out and breathe in the mountain vista.

Two ShellTAs, zipped together in poncho mode create a shelter nearly 3m long, which can provide protection for a casualty and two first aiders.

(Large clan tents, mountain shelters or bothy bags are used by most mountain rescue teams to provide an environment for multiple team members to stabilise a casualty. The ShellTA is not big enough for this role.)

For more on First Aid please try this site.

Thanks to Glossop Mountain Rescue Team for this image.

Production ShellTAs are longer than this prototype.

In an emergency (or just to have lunch out of the rain) two people can sit down side by side in the ShellTA. This is remarkably cosy. Tuck the fabric beneath you to help prevent the fabric from flapping but allow a small amount of ventilation.

To minimise heat loss reduce contact with the ground and sit on something insulating (eg sit mat, rope or sack). Huddle together to minimise your surface area and use all the insulation you have before you start to feel cold.

Each person gets a zipped window for venting or to admire the view!?

ShellTA over FurTech Trousers

One of the advantages of using the ShellTA as a poncho is that it’s easy to pull it over your head to protect your body and legs, rather than struggle into over-trousers. This is particularly useful in sudden heavy rain and occasional squalls.

How much of your legs it covers depends on how tall you are, but even very tall people can often get away with just protecting their lower legs with gaiters.

In persistent bad weather or wintry conditions it is prudent to use overtrousers or water resistant softshell trousers beneath the ShellTA to keep the inevitable condensation at bay. In summer rain try using the ShellTA over shorts to stay cool.

Pile / pertex softshells rely on being (relatively) warm when wet and quick drying. Body heat helps push moisture outwards when you are on the move, but this can seep back in when you stop and begin to cool. They can also be a tad warm as you climb out of the valley, even though their insulation is appreciated on cold and blustery tops.

The ShellTA adds an extra dimension to a Pile Pertex system, adding an option for warm and wet conditions, very wet conditions and providing shelter when you stop… all for less weight than a typical waterproof jacket and trousers.

A Buffalo sleeping bag system will also benefit from the ShellTA, used as a tarp for wet weather bivis.