A method for manufacturing a cellular geopolymer product, which method comprises the steps: (a) forming an activated geopolymer premix by addition to a geopolymer premix of an activator compound that initiates a condensation reaction in the geopolymer premix; (b) casting the activated geopolymer premix in a desired configuration; and (c) generating gas bubbles in the activated geopolymer premix as the condensation reaction proceeds and the activated geopolymer premix stiffens to produce a self-supporting cellular structure; and (d) curing the self-supporting cellular structure to produce the cellular geopolymer product, wherein in step (c) the characteristics of the activated geopolymer premix and the reaction kinetics of the condensation reaction are controlled to achieve formation of the self-supporting cellular structure.