I've used it with and without batting - without batting it does shrink up about 30% like their ads say - but with the batting the percent of shrinkage is...well, shrunk....since the bulkiness of the batting prevents the fabric magic from shrinking to it's full potential. In my experience the more steam you give it the greater the shrinkage is...when it first starts shrinking, it will be rather convoluted as someplaces shrink and others don't - keep moving the iron around to make sure all parts receive the steam requried and when it's all evenly shrunk, the fabric magic will again be flat.