Summer Weight Sweaters-- there is such a thing! They're almost always made from linen or a cotton-linen blend and are so thin they're a little see-through. Linen is a stiffer material than cotton, but it breathes so much better. The fibers are spread further apart so you're protected from the sun but you don't feel like you're wearing a heavy layer. Just think about the nomadic tribes in the Sahara. They're covered head to toe in thin layers of linen, protected from the sun but ever so cool (as cool as you can be in that kind of heat...)
This sand colored sweater inspired me to go all monochromatic. You can never go wrong with a tight color pallet and it's a refreshing break in the middle of Summer. Next time you're out, try on a linen sweater. I think you'll be surprised how light and easy it can be. Just be sure to ditch any layering pieces you're used to wearing underneath. It's Summer after all!