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Glass wool (UK) or fiberglass insulation (US) is an insulating material made from fibres of glass (fiberglass), arranged into a texture similar to wool. Glass wool is produced in rolls or in slabs, with different thermal and mechanical properties.
After the fusion of a mixture of natural sand and recycled glass at 1,450 °C, the glass that is produced is converted into fibers. It is typically produced in a method similar to making cotton candy, forced through a fine mesh by centripetal force, cooling on contact with the air. The cohesion and mechanical strength of the product is obtained by the presence of a binder that “cements” the fibers together. Ideally, a drop of bonder is placed at each fiber intersection. This fiber mat is then heated to around 200 °C to polymerize the resin and is calendered to give it strength and stability. The final stage involves cutting the wool and packing it in rolls or panels under very high pressure before palletizing the finished product in order to facilitate transport and storage. Glass wool
Glass wool is a thermal insulation that consists of intertwined and flexible glass fibers, which causes it to "package" air, resulting in a low density that can be varied through compression and binder content. It can be a loose fill material, blown into attics, or, together with an active binder sprayed on the underside of structures, sheets and panels that can be used to insulate flat surfaces such as cavity wall insulation, ceiling tiles, curtain walls as well as ducting. It is also used to insulate piping and for soundproofing.
Batts are precut, whereas blankets are available in continuous rolls. Compressing the material reduces its effectiveness. Cutting it to accommodate electrical boxes and other obstructions allows air a free path to cross through the wall cavity. One can install batts in two layers across an unfinished attic floor, perpendicular to each other, for increased effectiveness at preventing heat bridging. Blankets can cover joists and studs as well as the space between them. Batts can be challenging and unpleasant to hang under floors between joists; straps, or staple cloth or wire mesh across joists, can hold it up.
Gaps between batts (bypasses) can become sites of air infiltration or condensation (both of which reduce the effectiveness of the insulation) and requires strict attention during the installation. By the same token careful weatherization and installation of vapour barriers is required to ensure that the batts perform optimally. Air infiltration can be also reduced by adding a layer of cellulose loose-fill on top of the material.
The National Toxicology Program classifies inhalable glass wool fibers as "reasonably anticipated to be a human carcinogen". Some fiberglass products warn of "possible cancer hazard by inhalation". The European Union and Germany classify synthetic vitreous fibers as possibly or probably carcinogenic, but fibers can be exempt from this classification if they pass specific tests. A report by Health Canada, mentions unspecified studies on glass wool exposure that show long-term exposure to glass wool does not cause cancer in humans or animals. Evidence for these classifications is primarily from studies on experimental animals and mechanisms of carcinogenesis. Studies of fiberglass factory workers show significant increases in lung cancer but do not show clear exposure-response relationships and may be confounded by the effects of smoking. A 2002 summary by International Agency for Research on Cancer puts insulation glass wool into Category 3 carcinogen, "not classifiable as to its carcinogenicity to humans". 
Fiberglass will irritate the eyes, skin, and respiratory system. Potential symptoms include irritation of eyes, skin, nose, throat; dyspnea (breathing difficulty); sore throat, hoarseness, and cough.
Fiberglass is resistant to mold but growth can occur if fiberglass becomes wet and contaminated with organic material. Fiberglass insulation that has become wet should be inspected for evidence of residual moisture and contamination. Contaminated fiberglass insulation should be promptly removed.
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