Jackets of suits have a lining that commonly consists of several layers of cotton, silk and linen that are stitched to the fabric of which the suit is made. A decent jacket has camel or horse hairs in the lining to enhance the fit of the jacket around the upper body of the wearer. Those hairs have ‘memory’ and will follow the contours of the wearer’s body over time. However, the lining also makes a jacket heavier and warmer. For winter, full lining suits are perfect. But for the summer I prefer to wear suits of which the jacket only has the minimum lining in the shoulders and for the sleeves to keep me cooler.
The suit jacket below has lining for the shoulders and the sleeves and therefore wears much cooler than the full lining jacket above. Linen suits, such as the one below, are sometimes without lining which brings a very nonchalant look to the table.