You can move the right lightweight plastic material by injection molding inside the soft foam for strength, a lot of weight and cannot harm both on land and in the water.
Can be moved to a suitable lightweight material is a plastic injection molding. The compressed foam for strength Loads more And not dangerous to use both on land and in water.
Convenient movable proper light weight material is a plastic injection molding. Within the compressed foam to strength, support the weight a lot. And harmless to operate both on land and in the water!