Cathode ray tube (CRT) panel glass is processed into glass foams by using carbon and Mn3O4 as foaming agents. We investigate the foaming ability and foaming mechanism of the mixture by varying the composition and the temperature. Carbon load of 5 wt% inhibits the sintering of the glass powder, while 2 wt% carbon promotes the coalescence of pores during foaming. Carbon load of ≤0.4 wt% is suitable for achieving low density foams (0.15–0.23 g cm-3) with closed pores (75–100%). Foaming is initiated by the reaction between carbon and Mn3O4 and this is the main source of melt expansion. Reduction of cations in the glass melt, including Mn3+ dissolved from Mn3O4, makes an important contribution to the melt foaming at >800 °C. The main gaseous product is CO2 (67–95 vol%). CO appears above 800 °C and the concentration increases with temperature.