My perfect summer bag is the WM Summerlite. When it gets too warm, I can shake all the down into the baffles underneath me and just have a light covering. Also, the full-zip is essential for venting in the summer. And when nights get colder than I expected, I can adjust the bag to be warmer and also use the hood. I love this bag... it's so versatile! It's rated for 32 degrees but I'm a cold sleeper and would need to wear a base layer in and stocking cap to sleep in it under 40 degrees. I do tend to camp a lot of places that are warm during the day but high enough in altitude to freeze during the night. With the right sleeping pad and keeping some extra clothes nearby, I've almost always been able to take the 19 oz Summerlite along.