Abstract: Thermal and/or acoustic insulation product based on mineral fibers, obtained by internal centrifugation and attenuation by a high-temperature gas stream and by crimping, characterized in that it contains no devitrified and/or defiberized particles, the length of the fibers is at most equal to 2 cm, preferably less than 1.5 cm, and the fibers have a micronaire per 5 grams of less than or equal to 4, especially between 2.5 and 4, or a micronaire of less than or equal to 18 l/mim, especially between 11 and 15 l/mim, in particular around 12 to 13 l/mim.