Buddy said that PET bottles only last 20-30 years. But I read everywhere that they take 450 years to decompose. The question now is how long it takes for such a compressed PET bottle to no longer hold its contents due to cracks, etc.
According to a website that I am not allowed to link:
Polyester is used not only in the textile industry, for PE films and plastic beverage bottles (PET - PolyEthylenTerephthalate), the fine fibers are also suitable for insulation materials due to the good thermal value (thermal conductivity lambda(R): 0.034 – 0.041 W/(m·K)). The polyester fibers (insulating fleece) require no additives and flame retardants. They are thermally bonded during manufacture. These are pure elastic soft fiber materials which have a sound-absorbing effect. Polyester is skin-friendly or allergy-friendly, diffusion-open, rot-resistant, decay- and UV-resistant, and has a very low heat storage capacity. For several years, polyester fleece insulation has been replacing traditional insulation materials such as mineral wool and PU soft foam in the insulation of domestic hot water tanks. Polyester materials are used as compression felt boards in walls (cavity walls), wooden beam intermediate floors, prefabricated structures, and wall cassettes for technical applications (sound absorbers).
That means PET is not so bad as an insulation material.