FABRIC
When you buy a custom-made suit, most tailors will set their price based on the fabric you select. This should give you an idea of how important fabric selection is. It's the most fundamental aspect in a garment's construction. Most menswear is made of either wool or cotton. The fabric used affects: weight and texture, the way it drapes on the body, the way it feels after hours of wear, and the care it requires.
Fabric properties are important to ensure comfort, fit, flexibility and match.
Wool
Sheep's wool is the staple material for men's suits, jackets and dress trousers. It comes in many weights and weaves - the finer the wool the better the drape, insulation and feel. Wool is warmer than cotton and has a smoother drape over the body. It's more expensive to produce and requires more careful cleaning and maintenance, but will last the test of time.
Cotton
Some very casual items likeT-shirts and sweatshirts are made from knitted cotton rather than woven, which creates a looser, softer and more shapeless garment. Cotton is sometimes measured by thread count, however, the "hand feel" of the shirt is more accurate judge of how it will actually feel on your body.
Men's dress shirts and more casual trousers are ususally made from woven cotton fabrics. The best shirts are 100% cotton, but a cotton blend that incorporates a small amoutn of synthetic for extra durability, still has the same form-flattering draped and feel of the natural fibre.