Keeping Alvin Afloat

Syntactic foam, show here being mounted on the new Alvin human-occupied vehicle, helps make marine submersibles buoyant, even at great depth. The foam is made up of small balloons of glass, mixed with epoxy into a matrix and formed into blocks. The glass microspheres are capable of withstanding pressures up to a depth of about 6,500 meters, which represents 95 percent of the ocean.(Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)