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WHOI Engineer Rod Catanach positions a block of syntactic foam above the titanium personnel sphere of the Alvin submersible during its recent overhaul and upgrade, which included the addition of new foam capable of withstanding pressure at depths of 6,500 meters. The foam is made of hollow glass microspheres mixed with epoxy to make hard blocks. The microspheres make the foam buoyant in water, but in air, this block weights nearly 1,400 pounds.(Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)