A calcium silicate insulation product includes a calcium silicate hydrate matrix that is predominantly but not substantially all xonotlite, for example 51-90 weight percent xonotlite and 10-49 weight percent tobermorite. The insulation product also contains wollastonite, fines of lime and silica, and reinforcing carbon fibers. A method of producing the insulation product includes providing the components of the insulation as dry solids, blending the dry solids with water to form a slurry, filter pressing the slurry to form a pressed shape, and curing the pressed shape under steam pressure only until the desired proportions of xonotlite and tobermorite are achieved in the calcium silicate hydrate matrix.