Both, the housing and the potentiometer control as well as the rotary switch for selecting the source are made of anodised aluminium, while the front panel of the housing and the controls are milled fromsolidmaterial.
The rest of the vertical column is made from a material called syntactic foam - a solid made mostly of hollow "microballoons" - giving it enough buoyancy to float back up.
They did this by putting pieces of silicon or one of a number of other solid materials inside a shoe-box-sized cavity and zapping the material with microwaves from a metal tip.