Batt Insulation from JR Putman
Batt insulation comes in pre-cut panels and is used to insulate floors, walls, and ceilings.
This type of insulation is generally made of fiberglass or rock and slag wool, although there are also natural cotton varieties available for thermal and acoustic installation.
Fiberglass batt insulation is one of the most popular forms, as it tends to be fairly inexpensive and easy to install. If installed properly, this insulation can be effective, energy efficient, and long lasting.
Batts are precut, whereas blankets are available in continuous rolls. 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 vapor 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.