Thick-walled preforms are used to create containers that need to be strong, durable, and reusable. These containers are made through a 2-step stretch blow molding process. In the first step (injection process), plastic is injection molded into a preform - a compact, often cylindrical form with a threaded neck, designed for the specific container shape. In the second step (blowing process), the preform is reheated, placed in a blow mold, and expanded with high-pressure air to form the final container. 

Processing heavy, thick-walled preforms into refillable containers poses challenges during both the injection and blowing processes. Thick-walled preforms are difficult to cool during the injection process and challenging to reheat during blowing. 

One of the main challenges of the re-heating process of thick wall preforms is obtaining balanced temperatures across the wall thickness of the preform. If the temperature difference (delta T) between the internal and external wall is too large, it can lead to defects such as cold stretching pearlescence and heat haze. 

Cold stretching pearlescence occurs when the preform is stretched at a low temperature, causing a whitish, streaky appearance due to uneven stretching of the polymer. On the other hand, heat haze results from overheating, where excessive crystallinity develops in the material, leading to a cloudy or opaque appearance in the final container. Both defects negatively impact the quality of the final product.