I was wondering what to do when sewing in a zipper when you get to the bottom and there is almost a plastic substance at the bottom. I am making a sporty jacket and it has a separating zipper up the front. The last time I used one of these zippers I decided to use a larger needle (like 90 denim) and it did go through, but my sewing machine had to be repaired after that. Something happened to the timing and the repair was over $300 dollars. My thought is just not sew right to the bottom, but I’m worried it might look sloppy. This jacket is for my 15 year old granddaughter and you know how fussy they can be. Does anybody have any ideas?