We had an issue with the irregular and sharp-eadged bottle forms. These bottles are hard to cut in strings and the weak parts break the ropes.
We solved this by making a modified bottle cap with a bicycle tire tube inlet.
As the bottles ar pressurises, the wrinkles straighten out. When heating the pressurised bottles (at about 1bar), the wrinkles disappear and the odd shape of the bottle also straightens out ( almost as the bottle expends as a balloon.
You can check out more on our instagram – @preciousplasticlv
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