Long-strand, unbonded, non-combustible borosilicate glass fibres that are mechanically consolidated to form felt and bonded to a 12 micron foil facing. It is capable of withstanding severe thermal shock vibration. The material is stable in arduous environments. Being non-hygroscopic, it does not absorb moisture or vapours, or accelerate the corrosion of metallic components. Excellent thermal and acoustic properties make it suitable for use in many types of silencing and jacketing applications.