TPE bubble and voids generally refer to the hollow spaces formed within the thick-walled molded parts, as the shell of the molded part solidifies first during injection molding, resulting in insufficient melt material relative to the entire part. This leads to vacuum holes, typically occurring in areas of thick sections and at the injection point. These are referred to as bubbles or voids.

Generally speaking, if bubbles are found at the moment of mold opening, it is a gas interference issue. The formation of vacuum bubbles is due to insufficient plastic injection or low pressure. Under the rapid cooling of the mold, the molten material in contact with the mold cavity is pulled, resulting in volume loss.

In this sense, the term "bubble" is inappropriate, as there is no air introduced into the instant holes after molding. Bubbles resulting from this cause cannot be deemed defects in the molding process, but for opaque or colored products, most are not problematic. However, it is essential to eliminate bubbles in transparent products and at the root of the main runner of injection molding with straight gates.