Fiberglass insulation is a building material made from tightly-woven glass fibers. It is sold in large rolls known as blankets or batts and is the most widely used type of insulation in the world. The history of fiberglass stretches back more than a century and helps to highlight the potential benefits and drawbacks associated with this material.

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.

Manufacturing bonded glass fibre requires materials obtained from two sources:

“Post-consumer”: glass materials recycled from construction sites (demolition work, new construction and renovation) and from consumers’“blue boxes”.
“Post-industrial” (or “pre- consumer”): glass recycled from glass manufacturing plants’ waste (glass containers, flat glass and others). Includes materials that contribute to the reduction of dust and static electricity, ensuring a clean and easy installation.


Batts most commonly are compressed into plastic bagging. The size of the bags vary depending on the different types of batt width, length and thickness. Average size of a bag is 4ft. length x 16in. width x 16in. thick and weighing around 10lbs. The bags are then bound into bundles containing 5 bags.