UPDATE

I AM THE IMPERIAL WIZARD

Testing

Here is a picture of the models we used during testing.  We made these models to try and determine which design would produce more drag, allowing us to move easier through the water.  As you can see from the video below, you can tell the first model is the desire choice.

Model 1- Flap Design

Model 2- Ridge Design

Video of Testing the two models

Expanding Foam

http://hubpages.com/hub/Expanding-Foam-Insulation-Guide

An expanding foam could be used to make the "shoes" out of. The link shows a page explaining how expanding foam works and its uses.

WH Alternate Solution

Foam

Here is a link to a picture similar to the foam that we will be using for the project.
http://maxcdn.homeconstructionimprovement.com/wp-content/uploads/2009/06/extruded-polystyrene-insulation.jpg

CM Alternate Solution

Pictured above is an alternate solution. Note the flaps on the bottom and the foot placement cavity. 

WH Alternate Solutions

Alternate Solution 1

Alternate Solution 2

Alternate Solution 3