"Summertime and the livin' is easy..." Your clothes should be easy too—easy to wear and easy to care for. When choosing a summer-weight fabric for trousers, you'll want to look for textiles that are breathable, wrinkle resistant, cool and lighter weight than the fabrics generally used in trousers meant for cold-weather wear.
Cotton is probably the number one choice for men's and women's summer trousers, for its breathability and washability. Generally, the coarser the cotton material, the less dressy it is. For instance, the tight weave and smooth surface of cotton twill---also called chino---is dressier than cotton duck or canvas, which is often used for work trousers.
A drawback to lighter-weight dressier cotton fabric is that it wrinkles more easily than other cotton weaves, unless it has been treated with a wrinkle-resistant coating. This is a trade-off, because many permanent-press treatments make a fabric less breathable.
Heavier cottons like denim can be difficult to work with. They require heavy needles and form bulky seams, and they are not as cool to wear in warm weather.
Linen is almost exclusively a summer fabric, especially for trousers. Summer overturns the men's wear dictum that the more formal the occasion, the darker the fabric should be. In some summer occasions, even white trousers are dressy, especially when they are made of linen.
Linen trousers look crisp and snappy---that is, until you sit down. Linen is notorious for wrinkling easily. Wrinkle-resistant treatments are a necessity for pure linen trousers. A linen blend resists wrinkles to some degree, but is heavier in weight than pure linen.
Summer-weight wool may seem an oxymoron, but tightly woven lightweight wool can be surprisingly cool. The longer the fibre used to make this type of wool, the softer the finished fabric. Wool sheds wrinkles, comes in classy traditional patterns and looks great. Consider using washable wool fabric for trousers.
Summer wool trousers typically come in fairly light colours---light greys and browns, for instance, They often sport a pattern such as pinstripes, windowpane plaid or muted glen plaid.
Silk twill is heavy enough to be used in trousers, especially trousers of a loose, flowing pattern. Some silk fabrics are washable, but generally silk requires more care—including ironing, hand washing and dry cleaning—than other fabric types.
Silk is often used in blends with other fabrics, where its strength and draping ability is an advantage. Compared ounce-for-ounce, silk is as strong as steel—if you could make a steel fibre as thin as silk.
Blends of natural and synthetic fibres offer a wide range of drapability and crispness and do not wrinkle as easily as pure linen, wool, cotton or silk. The natural fibres tend to be more breathable; the synthetics more wrinkle-resistant. Polyester does not make a good fabric for summer trousers; it retains heat and does not breathe well. But a blend of polyester and a more breathable fabric, like cotton or linen, is quite suitable for summer trousers.