Mountain weather is fickle friend; even on sunny days the wind can quickly cool you. The key to staying warm is to stay dry, because wet clothing leads to heat loss through evaporation and impaired insulation. Wearing many thin layers traps heat far more efficiently than one piece of bulky clothing, and will allow you to regulate your body temperature and reduce perspiration. Even if you set off in shorts have some extra layers in your rucksack.
The layering process
The layer of clothing next to the skin (the base layer) should be snug, porous and made from a performance fabric, such as polypropylene, that wicks perspiration away from your skin to the mid-layer. Merino wool is gaining in popularity because it smells less, absorbs moisture well, is soft, biodegradable, and doesn’t melt easily. It is however heavier, slow to dry and expensive. Avoid cotton because it traps moisture before it hits the jacket, making you cold.
the mid-layer should be a thicker synthetic fleece to hold in heat, yet still able to wick moisture away from the body. The insulating layer can be a thicker fleece or, if you are doubtful about the weather, a lightweight duvet jacket can be carried e.g. Mountain Equipment Trango jacket. It is a myth that your head loses any more heat than elsewhere on your body and in fact it is your arm pits and grains that probaly lose the most. Hats should be carried all year round, and a sun hat is vital. Gloves are also essential and, generally, bulk equals warmth, although you lose dexterity. There is more information on staying warm in the winter section.
These supposedly provide an outer and insulating layer in one. They are soft to the touch, highly water resistant, wind resistant, highly breathable and often stretchable. While not 100 per cent waterproof, a soft shell delivers twice the breathability of Gortex, however they do take a long time to dry out when wet and you will then feel the cold more. The decision to wear soft shells or conventional clothing depends on the activity. If rain is likely, a conventional waterproof jacket is important, but for aerobic activities in cold, dry, high activity situations, soft shells may work well. A soft shell - evaporation uses heat therefore the more breathable a jacket is the cooler you will feel.
The best way to minimise knee trouble is to have strong muscles supporting the knees, especially the quadraceps/thighs, this will allow your muscles to take some of the load off your joints. However Trekking poles can help, below is information on trekking poles.
They’ll help protect your knees, make it easier to get across streams, save you energy and generally speed you up - but only when they are adjusted to the correct length. Poles do have a downside: they transfer the stresses to your elbows and shoulders, keep your hands full, increase total energy expenditure, and there is evidence that they prevent novices from learning essential balance. Alun Richardson Training Officer for MI says "I rarely use them on simple walks, but when the going gets tough especially downhill they are invaluable".