. Hydro Flask - Standard Mouth Flex Straw Cap. Color Black. On sale for $11.19. MSRP $14.95.. 4.2 out of 5 starsBest SellerBrand NameHydro FlaskProduct NameStandard Mouth Flex Straw CapColorBlackPrice$11.19MSRP: $14.95Rating4Rated 4 stars out of 5(91)