What did you use to "shade" out your windows?

I covered up all but 6 of my windows already and I'm planning on what I'll do with the remaining 6.

My current plan is to block off the bottom half, insulate it and just put a wall around it so only the top half will remain and I can open the window up/down for air.

I suppose I could just paint the bottom half black or get some foam insulation of the right thickness and paint it black before I insert it in the cavity, but I'm trying to see if any of you have done something differently that worked better.

I'm pretty set on blacking out the bottom half of my windows, but am open to suggestions on how to accomplish that, maybe there's some plastic insert that's already black that I can just slide down? or a rubber mat that I can glue to the window? Open to ideas.