Cotton: The all time favorite cotton is the best deal in summers. It is soft, breathable, soaks sweat, allows the body heat to escape, thus giving you cool feeling. It is available in lots of qualities, colors and blends. As it wrinkles a little, you can opt for cotton and polyester blend with a bigger proportion of cotton. Cotton will keep you cool and polyester don't needs ironing.
Linen: Pure linen that comes in different weights from ultra thin to heavy, is ideal for summer clothing- lighter ones for blouses and dresses and the heavier for summer jackets and slacks. Linen is strong, durable, absorbs perspiration and dries quickly, doesn't lint and softens as it ages. It feels cool and comfortable more than any other fabric. However, it wrinkles a lot so you can go for the luxurious blend of linen and cotton.
Rayon: Rayon derived from cotton linters or wood pulp, comes in many types-viscose, high wet-modulus, lyocell (tencel) etc. and is often blended with other natural and synthetic fibers. A comparison of rayon with other fibers show that rayon is a a good conductor of heat and thus is appropriate for summer clothing. It is one of the most absorbent fabrics, even more than cotton or linen.
Denim: Denim is also a popular fabric for summer times. It is made from tightly woven cotton and is breathable, sweat-absorbent just like cotton. However, when compared to pure cotton, denim is more heavier than it. Therefore, one must go for lightweight denim in order to keep cool in summers.
Lightweight wools: Not many people know that, with correct engineering, wool can be made to act as a very cool fabric for summer heat. The astonishing and interesting fact about summer suits is that they are made of light weight wool apart from cotton and linen. Wool has excellent insulating properties and as such it keeps wearer warm in winter and cool in summer provided the fiber diameter, length, spinning technology etc. are appropriate to produce 'Cool wool'.