Yes, you can steam clean a 100% polyester couch. Steaming is a safe and effective method for cleaning polyester fabric, as it helps to remove dirt, stains, and odors without causing damage. However, it is important to follow the manufacturer's instructions and guidelines for steam cleaning your specific couch. Make sure the steam cleaner is set to the appropriate temperature and use a low-pressure setting to avoid excessive moisture or heat that could potentially damage the fabric. Additionally, always test a small, inconspicuous area of the couch first to ensure that the fabric reacts well to steam cleaning.