Rana should buy cotton shirts rather than buying synthetic ones, for summer.
During summer season, the water cycle starts where the evaporation of water takes place in a continuous manner. As there is an increase in evaporation therefore more water molecules start accumulating in the air. As a result, when we starting perspiring / sweating , there remains no space for our sweat which is water molecule, to evaporate and hence it remains on our body surface.
Now if one wears cotton clothes then cotton being a good absorber, tends to absorb the sweat quickly and release it to the environment thus making us feel cool.
While synthetic clothes couldn't release the sweat quickly, so it keeps the body warm which becomes unbearable for summer days.