Blue Lug Reflector Triangle - Color picked at random
4 inches wide by 3.5 tall - Blue Lug, the best bike shop in the world, makes these reflective triangles.
They come with a shock cord and adjuster and it's easy to find a way to hang it on your bike. Super reflective and neat colors, but you don't get to pick which one you get. If you have to have a particular color, please buy directly from da Blue Lug.