The Phanpy Breast Hot Cold Compress Pad is designed to provide relief for breastfeeding mothers experiencing engorgement or discomfort. It offers long-lasting temperature maintenance for both hot and cold therapy. The S1/S2 designation likely refers to size or compatibility with specific breast pump models. This pad can be used to soothe sore nipples, stimulate milk let-down, or reduce swelling and pain associated with breastfeeding.