GTS Expedition Molded Foam Kayak Seat - No Pack The GTS Expedition fits any sit-on-top kayak 18 tall backrest and 2 thick seat bottom provide unrivaled support and comfort with a 6 point rear attachment system for customizable comfort Deep comfort/drainage channels in the seat bottom funnel excess cockpit water Built-in mesh bungee pouch for secure gear storage. Seat Back: 18L x 21W Seat Cushion: 16L x 18W x 2H