To provide an inorganic-fiber heat-insulating material for blowing, which suppresses a decrease in density by making a void in a heat insulating layer smaller when the heat insulating layer is formed by blowing the inorganic-fiber heat-insulating material into a ceiling, and which can reduce variations in the density.

When the distribution of sizes of many pieces of small mass-like cotton constituting the inorganic-fiber heat-insulating material for blowing is measured by performing sieving by means of metal wire sieves which have nominal apertures of 31.5 mm, 11.2 mm and 6.7 mm specified by JIS Z8801-1, respectively, the ratio of the pieces of small mass-like cotton remaining on the sieve with the nominal aperture of 31.5 mm is 5 wt.% or less; the ratio of the pieces of small mass-like cotton passing through the sieve with the nominal aperture of 31.5 mm and remaining on the sieve with the nominal aperture of 11.2 mm is set to be in the range of 45-60 wt.%; and the ratio of the pieces of small mass-like cotton passing through the sieve with the nominal aperture of 11.2 mm and remaining on the sieve with the nominal aperture of 6.7 mm is set to be in the range of 15-30 wt.%.