A plastic vapor barrier should completely cover your basement to prevent water from penetrating through the walls. This typically goes before installing insulation to prevent moisture from building up and becoming trapped on the inside of your insulation, where it can collect and lead to mold damage. Installing insulation after the vapor barrier allows for any moisture to exit the walls for better ventilation.

Fiberglass is the best insulation for HVAC ducting because it's inexpensive, widely available, versatile, and long-lasting. Fiberglass also offers acoustic insulation in addition to thermal insulation, which can contribute to a more peaceful home environment. You can use other materials like mineral wool, but fiberglass is the industry standard.

Unfaced wall insulation is easier to cut and install, making it the better choice for a DIY project. It’s also more affordable. But if it’s unfaced, you’ll likely need to add a vapor barrier to reach your desired R-value and efficiency, as it doesn’t offer any moisture barrier.

Faced insulation uses paper or foil to create a built-in barrier and doesn’t require an extra step. It’s also more fire-resistant and safe. But it’s quite a bit more expensive and a little bit harder to work with as a DIYer.

Adding insulation to ceilings is an excellent way to increase the energy efficiency of your home. If your home's layout is such that you need insulation in the ceilings rather than in the roof, it's likely that at least some insulation already exists in the space. However, each additional inch of insulation you can add boosts the R-value by between 2.2 and 4.2.