The bottles of mineral water are made of PET and PVC, and PVC is generally used more.
The hardness of the bottle is only relative to the thickness. Take a 500ml bottle as an example. As long as the bottle cap is unscrewed and it is not easy to squeeze out the water in the bottle, it is considered qualified. But pay attention to the bottle. Generally, those with chromatic aberration, impure color, impurities or black spots are recycled materials.