To ensure quality installation, whether you hire a professional or do it yourself, you should also look for voids and gaps, and fluffing.
Voids and gaps occur if insulation is installed at too low a density or if a cavity isn’t completely filled. Voids also occur if the installation holes are improperly located between the vertical framing studs or if there are too few fill holes.
Fluffing occurs when insulation is installed to minimum thickness but not to minimum weight requirements. The result is a less dense application of insulation that requires fewer bags. When insulation is fluffed, air passes more easily through it. This means increased heat loss. Additionally, the fluffed loose-fill insulation will eventually settle, resulting in a loss in thermal resistance or R-value. Fiberglass is more “fluffable” than cellulose or rock wool.
Intentional fluffing by unscrupulous contractors has been a problem in some parts of the country. To avoid these problems, compare bids from several contractors to see how many bags they specify. Count the number of bags used during installation, either by you or a contractor, and compare it to the instructions on the bag. The manufacturer should specify the amount of insulation required to obtain a particular R-value per square foot (or square meter) of space.
Source: EERE, U.S. Department of Energy