The level of waterproofing for taffeta fabric with a silver coating can vary depending on the specific fabric and the quality of the coating. Generally speaking, taffeta with a silver coating can provide a moderate level of water resistance, but it may not be completely waterproof.
The silver coating on the taffeta fabric can help to repel water and prevent it from seeping through the fabric, but it is not completely impenetrable to water. If the taffeta fabric is exposed to heavy rain or submerged in water for a prolonged period of time, water may eventually penetrate the fabric.
If you need a high level of waterproofing for a specific application, it's important to look for fabrics that are specifically designed for that purpose, such as those that are coated with a waterproof membrane or laminate.