55±5% Crystallinity Stable Viscosity PET Resin for Natural Mineral Water Bottles Problem Producers of natural mineral water report random wall-thinning, neck cracking and uneven bottle weights that appear without any change in machine settings. Scrap spikes on a single shift, and the cause is hard to trace because the bottles look acceptable on the conveyor. Lightweighting programs make this worse, because thinner walls reduce the safety margin that used to hide resin