Antizipper or Zipperless Design:
On this topic, I am more of the gatherer than the writer.
Zippers can ruin your rocket weekend. Designs meant to reduce zippers are all over the place. Zippers happen when parachute deployment occurs at a high rate of speed or when your shock cord is too stiff to absorb the shock of deployment. If the rocket is designed using traditional methods, the shock cord can rip a good slice down the side of the body tube.
The photo above was posted by @tim cubbedge
and is a great example of a zippered tube.
This high-speed deployment has happened due to early or late ejection with a ballistic trajectory. Either case is a deployment at a higher-than-desirable speed. The main problem is a whipping effect with a long piece of shock cord against the side of the body tube. The stress on the shock cord is imparted on the body tube, resulting in a zipper.
So how do we prevent them? The best method I have seen is a "zipperless" design. The best article I have ever seen on the topic was by Stu Barret. It can be found on the Info-Central:
I also attached a PDF copy.
Another good read is the Peak of Flight 290:
I know what a zipper is, in regards to rocket damage, but I’m wondering how this zipper proof design is achieved.
The best solution is to avoid zippers, but you can also repair them,
but that is a topic for another day.
If you have a better solution, please post it in the comments thread.