The next topic is clothing. I recommend using cycling clothes because they are made of fabrics which actively conduct sweat away from the body. Besides, even if we are sweaty, those fabrics still look fresh. They are also easier to wash and dry quicker than cotton clothes. Moreover, cycling shorts are cut to provide maximum comfort. They have antibacterial pads which help to avoid sores and scrapes. When dressed in these shorts, remember not to wear pants because otherwise the seams will chafe the groin area.
I advise against wearing cotton t-shirts since they tend to absorb sweat. After a whole day of cycling, you end up with unpleasant salt stains and next day, they just stink. Generally, they are not fit for such expeditions.
When you go to the mountains, take some warm clothes. At high passes there may be breaks in the weather and during downhill rides it gets really cold (which is why some useful items may include warm gloves and... cotton wool – to put into ears). In cold weather, it is good to wear several layers of clothing. If it gets warmer, just take off one layer. Sweatshirts made of Polar 100 or 200 are recommendable, but remember that they are not windproof, so put some windbreaker jacket on top, for instance Gamex. Such a jacket has got yet another advantage – it can be easily hidden in a pocket when it is not needed.

Clothes (jacket + trousers) made of membrane fabrics (Goretex, Sympatex, Bretex, NoWet, Thermoactive, etc) are the best choice for rainy days. They are classified according to the level of water vapour permeability. Highly waterproof fabrics are characterised by low vapour permeability. In this case, at moderate effort, the membrane will not be able to draw all the sweat away.