T Sacs are a tea bag filter to use with your loose tea leaves. They are large enough to give the loose tea room to expand during the brewing process, yielding a more flavorful cup or pot of tea. They are compostable. 100 t sacs in a package. Size 2 is good for a small pot or a mug of tea. Size 3 is for a large pot of tea. We also use size 3 to make herbal bath bags for sore muscles.