Here's my preferred helmet for downtown and neighborhood riding. Notice the excellent ventilation. It's made of resin-impregnated organic fiber strands, it's stiff, and the 2-ply woven fabric gives it good crush/impact absorption. It stays on my head, has an integral sweat pad (removable for cleaning), and is very cool in 100˚F temperatures. It even has an ANSI sticker in it.
I would love to see a cycling-specific helmet manufactured from the same material.