Glass wool

In order to accomplish the formation of small gas cells in man-made thermal insulation, glass and polymer materials can be used to trap air in a foam-like structure.

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.

Gaps between batts (bypasses) can become sites of air infiltration or condensation (both of which reduce the effectiveness of the insulation) and require 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.

[7] Scientific evidence demonstrates that fiberglass is safe to manufacture, install and use when recommended work practices are followed to reduce temporary mechanical irritation.

In June 2011, the United States' National Toxicology Program (NTP) removed from its Report on Carcinogens all biosoluble glass wool used in home and building insulation and for non-insulation products.

[9] Similarly, California's Office of Environmental Health Hazard Assessment ("OEHHA"), in November 2011, published a modification to its Proposition 65 listing to include only "Glass wool fibers (inhalable and biopersistent).

All fiberglass wools commonly used for thermal and acoustical insulation were reclassified by the International Agency for Research on Cancer (IARC) in October 2001 as Not Classifiable as to carcinogenicity to humans (Group 3).