Here’s a hint: It’s not linen! My go-to dress every summer when it’s too hot to think is a knit, your favorite-T-shirt-type-of-material, doesn’t-show-your-sweat dress. My favorite is a black number I bought years ago at Grand Central Clothing on University Blvd. Year after year, it is my best friend who has my back, even when the rest of me feels like I’m doing Bikram yoga, except without the actual exercise part.