Anti-zipper foam

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Well-Known Member
Feb 1, 2009
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Tonight I was getting a few rockets ready for this weekends CMASS launch. I have 2 new rockets that I built with kevlar thread for the shock cord. The kevlar thread caused a nasty zipper in my Stormcaster a while back. So I am trying a new anti-zipper technique. I bought some foam decorations at Wally Mart for 67 cents each. The foam is slightly denser than Nerf foam. I cut a piece and cut a slit sideways and slid it over the cord. I positioned it so that it always makes contact on the body tube edge. I hope it is enough to prevent a zipper!! I will see how it withstands the exhaust gases.

These are the foam doorknob decorations. I got the idea from Giant Leaps anti- zipper foam ball.

Depending on the material, you might want to add some sort of protection from the exhaust.

I have added several anti-zipper measures to my Kevlar. One was based on a soft rubber ball protected by some car airbag cloth; a few use packing bubbles covered in cloth tape. I now generally just wrap some cloth tape around the cord where it touches the tube.