The main reason for the appearance of white bubbles in the product, which are either empty or foam when dissected, is the presence of air in the silicone material. During the high-temperature and high-pressure vulcanization process, the pressure is released too quickly, causing the air inside the product to expand, or the vulcanization time is too long or too short, the molding temperature is too high, and there are too many exhaust times. The second reason is due to material shortage. Some silicone product factory staff arrange the material unevenly before pressing the mold, Some are more and some are less, resulting in a shortage of materials in the processed products. During the vulcanization process, high vulcanization temperature and low machine pressure can also lead to product defects. When the molding temperature is too high during the processing, it will accelerate the vulcanization of silicone product rubber material, and the flow performance of silicone product rubber material in the molding mold will decrease, which will lead to smaller size and thicker thickness of silicone product, resulting in defects.

Regarding silicone rubber, please check the details:
https://www.rtvsilicone.net/product-high-strengh-liquid-silicone-rubber-iota-28-series-.html