It can be easily broken and produce fine suspended particles. If the glass wool is of poor quality, you'd better use plastic bags or non-woven fabric to wrap it when using. So you must choose brand whose products are of good quality. Also if it is for the acoustics, it will do harm to the human body if inhaled into the lungs. So be sure to choose a renowable brand o centrifugal glass wool.
A large number of people think that glass wool boards are harmful and that it will cause itch when contacting with the skin. And the effect is not obvious used in the surface, so it is generally used in the wall sandwich. They are harmless for wool boards have been checked, and only those which have passed the national inspection are allowed to be sold for home use. But do not use it in the surface as it is fiber products.
