CSD can stand for carbonated soft drink, and the cap on a CSD bottle is a plastic cap that seals the bottle. CSD stands for carbonated soft drink. CSD bottles are often made from PET, a lightweight material that is easy to handle. PET bottles are replacing glass bottles because they are less likely to break and are easier to return. Plastic bottle caps are made using injection molding machines. In this process, plastic is heated until it melts, then injected into a mold. Pressure is applied to maintain the shape, and the bottle cap is then cooled and molded.