This is my Civic.
This is thin lauan plywood, primed and painted.
The wire loops going back into the grill are a bit ghetto but I'm good with it.
Been meaning to redo this in plexiglass so you can see the "H" logo but other projects keep getting in line ahead of that.
My lower grill is about 2/3 blocked. Never had to open it up any more than that all summer, including using a/c on occasion. In winter I'll probably have the lower grill about 80-90% blocked.