Mould tool to be arranged in a press with essentially parallel press surfaces for production of rigid expanded polymer embryo bodies, the mould tool comprises a first mould member and an second mould member that are moveable with respect to each other in a direction perpendicular to the press surfaces, and sealing means providing an essentially hermetic seal between the first and second mould member during at least a portion of such a relative motion, thereby defining a closed mould cavity of variable volume, wherein the first mould member defines at least a portion of the mould cavity volume and comprises an outer peripheral edge, and the second mould member comprises a rim that closely circumscribes the outer peripheral edge of the first mould member and wherein the sealing means is arranged in the gap formed between the rim and the outer peripheral edge.