Normally an unprotected surface of mineral wool products like Rockwool with more or less loose fibres will not be accepted in working or living rooms. Therefore the surface should be protected in the final application.

In principal this can be done by using materials like glass fleece, aluminium foil, plastic sheets or foils or metal. Doing this, the acoustic properties of the Rockwool application will be changed. The sound insulation will in most cases increase.

The effect on the sound absorption mainly depends on the airflow resistance of the surface protection. Closed surfaces will reflect more or less of the incoming sound waves and the sound absorption will therefore be reduced. Very thin and loose mounted foils (e.g. 20 - 40 μm foil) have a more or less neglecting reduction of the sound absorption coefficient while a 0.5 mm metal sheet will reduce the absorption towards zero.

Metal foils of example 20 - 80 μm aluminium will act almost like metal sheet in sence of acoustic reflection.

Perforated metal coverings with a effective free area of more than about 25 % (e.g. a perforation with 3 mm holes with a distance of 5 mm, free area >30%) result only in a minor reduction of the sound absorption coefficients.

It is recommended to make sound absorption measurements to get the actual values for the sound absorption using a specified surface protection, when sound absorption is a crucial issue in the application.