Abstract: A hardened asbestos-free, porous, calcium silicate filler material for an acetylene storage vessel is made by mixing quicklime with water to form a first mixture. Then ground quartz silica is added to form a second mixture. A fibrous reinforcing material is blended in to form a third mixture. A precipitated silica (or synthetic silica) is added and homogenized to form a fourth mixture. The fourth mixture is transferred into a cylinder to be filled and is cured under saturated steam pressure. Thereafter, the cylinder is dried. A gas storage cylinder so formed has a monolithic dry mass filling a metal shell. The mass has a porosity of about 88 to 92%, a density in the range of 250 g/l to 350 g/l, and a crush strength of 250 to 550 psig.