To make polyester waterproof knit fabric, manufacturers typically use a process called coating. This involves applying a waterproof coating, such as a polyurethane or a polyvinyl chloride (PVC) coating, to the surface of the fabric. The coating is applied through a variety of methods, including roller coating, knife coating, or spray coating. The fabric is then heated to cure the coating and make it adhere to the fabric. Additionally, a DWR (durable water repellent) treatment can be applied to the fabric, which helps to repel water and prevent the fabric from becoming saturated.

To make polyester waterproof knit fabric, several steps are typically involved:
Knit the fabric using polyester yarns.
Apply a waterproof coating to the fabric. This can be done using a variety of methods, such as coating the fabric with a waterproofing agent, laminating it with a waterproof film, or impregnating it with a waterproofing solution.
Allow the fabric to dry and cure before using it.
It is important to note that not all polyester fabrics are waterproof, and the effectiveness of the waterproofing treatment can vary depending on the method used and the quality of the fabric. Additionally, some waterproofing treatments can affect the breathability of the fabric, so it's important to test the fabric before use to ensure it meets the desired performance criteria.