Black speaker cloth works wonders, really helps kill the light and still allows for air flow.Nah I can't hook ducting up to it nor do I want to to b honest I'm looking for something flat I just didn't want to buy entire roll of mylar for a 2 inch hole ya know?
thrift stores, buy old speakers with black fabric, bust 'em up be merryI like this idea, but where would one go in north america for speaker cloth?
that reminds me, darkroom vents will work, and they come in round shapes. something to keep in mind.if you want something made for the purpose, do a search for back draft shutters : http://au.alibaba.com/product/368687812-Back-Draft-Shutter-Match-For-Duct-Fans.html might cost a bit more if you're ordering less than 3000 mind !