My 2nd tip for staying cool this summer is pairing that paper-thin blazer with an equally light t-shirt. Again, it's not rocket science, but it goes to show that throwing on a blazer with your t-shirt/jeans combo can elevate your look tremendously. Just remember: you want your outfit to look intentional, so be sure the fit of your jeans and t-shirt are on point to avoid looking like the blazer was your girlfriend's idea. 

Blazer: Suitsupply (just like this one) | T-Shirt: J.Crew Factory | Jeans: DL1961 (super cheap pair here) | Shoes: Suitsupply (check these out) | Pocket Square: The Tie Bar (similar here) | Watch: Omega (vintage) | Sunglasses: RayBan