The best oblong scarves for summer are either a linen-cotton or a rayon blend. I like cashmere too, but it can feel too fall for me sometimes. I don’t recommend a large 100% silk scarf for summer because it will stain and ruin quickly. The best oblong scarves to be used as jackets in the summer are large. I like mine anywhere from 38 inches wide to 53 inches wide and 60 inches long to 80 inches long, give or take an inch or two.