Improved SBS bladder & bite valve for 2019. Slide top allows whole bladder to open for easy cleaning and fast filling. Leak proof. Double-welded pouch seams. Odorless, tasteless polyurethane bladder. FDA safe material. Soft silicone mouth piece with drink through new improved bite valve. 2 ways to stop waterflow; bite valve or twist shut off. Volume indication guide. Lightweight design for minimal bulk in your pack.