5/8 backing. This slides into a channel between the two sashes at the interlock as an air dam. It's a very stiff backing, most likely sold in strips as opposed to rolls. See attached photos.
Client is looking for 300
Paul from SWISCO responded:
March 26, 2015
Thanks for posting. This is pretty big. The closest pile we have to your dimensions is our 58-050, which has a 7/16" base. Could this work on your window?