I think we need to quantify these products in terms of risk. Anything used by the building trades has a risk statement. Solids, liquids and gasses are classified and commercially their use follow quite rigid guidelines. As far as I can discover the products mentioned do not cause cancer. Even the glass based spun products are classified as irritants, and are not directly carcinogenic. Asbestos - probably the most highly dangerous product that has been used for buildings for quite a while now is not in itself carcinogenic, but the fibres can embed in delicate areas of the body like the lungs, and increase the incidence of cancer related illness. MDF panels use formaldehyde in their manufacture and this outgassed into the rooms it is used in, and of course is present in the dust caused during cutting. We must correctly assess the risk of using these products. Glass fibre insulation in a cavity that is sealed is not inherently a problem. Used inside duct work to deaden sound would be foolish because the airflow will be contaminated. We just need to be sensible. More people have their health damaged by exposure to loud sound than ever develop cancer as a result of being in a studio with insulation fitted. Our lungs have a good capacity to filter out contaminants. It's just that everyone will have stuff in their lungs they shouldn't - and some of it could add to the cancer risk. If you are at risk, you need to reduce that risk - but it needs to be looked at properly.