This is replacement tacking material used when replacing your convertible top. Most cars use 2 different size tacking material to staple the top to, this is the style that is usually used on the top side of the front header bow where the pads attach as well as on some bows at the edges. It is 1/2" wide and 3/8" thick plastic material that is made to replace the old tacking strips on your car. Your original tacking material could have been a compressed cardboard or any number of different materials, they all fall apart after time and the new plastic tacking strip holds staples better and will never rot away.
This material is sold by the foot.