Radiant barriers and insulation serve different purposes, so one is not inherently better than the other. Radiant barriers reflect radiant heat, helping keep spaces cool, especially in hot climates, while insulation slows heat transfer through conduction. For optimal energy efficiency, it’s best to use both together. 

Radiant barriers can enhance the performance of insulation by preventing heat gain in the summer and heat loss in the winter. The choice between them depends on specific climate conditions and the building’s design requirements.

You should not use spray foam insulation in several specific areas. Avoid applying it in spaces exposed to high temperatures, such as near electrical boxes or recessed lighting, unless the foam is specifically rated for such use. Applying foam near electrical boxes can damage the wiring, and using it too close to lightboxes or recessed lights creates a potential fire hazard. Additionally, do not use spray foam in areas prone to shifting or movement, as this can lead to cracks and gaps in the insulation. Finally, open-cell foam is unsuitable for use below ground or in areas exposed to moisture because it can absorb water, which compromises its insulating effectiveness.

You do not always need to remove old insulation before adding new. If the existing insulation is in good condition—not wet, physically damaged, moldy, or infested with pests—you can add new insulation directly on top of it for a compounding effect. You can also mix different types, such as adding blown-in insulation around existing fiberglass batts.

However, removal is recommended if the old insulation is compromised by water damage or pests. You should also remove it if you plan to install a different type of insulation, like switching from roll or batt insulation to spray foam. If the existing insulation is very old or damaged, you will likely get more benefit from removing it and starting fresh.

Fiberglass is considered a favorite garage insulation choice due to its combination of affordability, ease of installation, and overall effectiveness. Fiberglass provides good thermal resistance, helping regulate garage temperatures and minimize heat transfer. Additionally, fiberglass is moisture-resistant, reducing the risk of mold or mildew formation.