Abstract: A method of manufacturing a capsule 12 for holding a substance 14 includes providing a capsule body 2 having a closed end 5 and an opposed open end 6; providing a diaphragm 4 having a closed end 7 and an opposed open end 8; partially filling the body 2 with substance 14; providing a gas-tight chamber; providing a nitrogen gas environment within the chamber; applying a partial vacuum to the chamber; supporting an outer side 43 of the body 2; supporting an inner side 102 of the diaphragm 4; while supporting the body 2 and the diaphragm 4, inserting the closed end 7 of the diaphragm 4 into the open end 6 of the body 2 until regions of the body 2 and the diaphragm 4 overlap one another, thereby closing off the open end 6 of the body 2 and forming a chamber 104 within which the substance 14 is held; and heat welding the overlapping regions of the capsule body 2 and the diaphragm 4 to one another to hermetically seal the chamber 104.