OTTER - Watertight to 100 Feet. The Otter Box was designed to be durable. The moulded fibreglass reinforced resin body is virtually crush proof. It will go anywhere and return one piece. The stainless steel hinge pin will not corrode in salt walter, the neoprene seal creates the perfect watertight barrier and the closed cell liner protects contents from damage. The 3500 Series is 21 x 13 x 10 cms in size.