Shaping metals as a foam modulates their physical properties, enabling attractive applications where lightweight, low thermal conductivity, or acoustic isolation are desirable. Adjusting the size of the bubbles in the foams is particularly relevant for targeted applications. Herein, a method with a detailed theoretical understanding of how to tune the size of the bubbles in aluminum melts in situ via acoustic pressure is provided. The description is in full agreement with the high-rate 3D X-ray radioscopy of the bubble formation. The study with the intriguing results on the effect of foaming on electrical resistivity, Seebeck coefficient, and thermal conductivity from cryogenic to room temperature is complemented. Compared with bulk materials, the investigated foam shows an enhancement in the thermoelectric figure of merit. These results herald promising application of foaming in thermoelectric materials and devices for conversion of thermal energy.