Durable, weather resistant to avoid becoming sogging wet and reflective are good. You don't want to add an insulating effect since it messes with the bird's ability to regulate its own temperature. I don't believe "neck warmers" are a good idea for the same reason, perhaps a mesh fabric to help avoid heat retention.
Good ideas I'll have to see exactly what they have available at the store. The neck warmers were a joke btw lol
Cream Crested Legbars, BCM, Rhodebars, bearded silkies, good laced/buff laced polish, black/lavender ameraucanas
Bourbon red, red bronze, royal palm, mottled black
I also make hen saddles, PM me for details!