Tri-Window Mask: Patented single lens with Edgeless technology on sides (three lenses,) which increases field of vision dramatically. Crystal, liquid silicone injected skirt and strap. Double skirt edge comfort seal. Low volume. The 2-buttom Tec buckle adjustment system not only convenient for buckle and strap adjustment but more secure and durable use. Buckles attaching with skirt, not with frame, makes swivel function more flexible and fits a wide range of face shapes. Ideal for MEDIUM face (face seal size W4 3/4 * H3 1/2.) Tempered glasses for Safety. Made in Thailand. Mask with built-in purge offers another channel to breath air out and keeps mask clear of water. Moreover, with channeled skirt design it directs bubbles away from view. Not mention of side-view and edgeless windows to broaden your panoramic view.