Fiberglass insulation isn't expensive nor hard to install. If, however, you have metal walls or beams, then installing this type of insulation may be an issue. Like most insulation, the fiberglass type doesn't adhere to metal, so follow the instructions below to effectively fasten it.
Step 1 - Clean the Metal
Metal has a habit of becoming oily or wet with condensation. This makes metal difficult to affix anything to. Clean the metal surface with a rag, spray with acetone, and wipe off.
Step 2 - Apply Adhesive
Polyurethane is safe to use on metal, won't cause it to rust and will actually help to protect it against rust. Spray the polyurethane onto the side of the metal where you want the fiberglass insulation.
Step 3 - Stick Fiberglass Insulation to Metal
Wait for the polyurethane spray to dry on the metal, and then use the sandpaper to rough it up. This creates a layer of textured polyurethane which will aid in sticking the fiberglass insulation to it. Spray polyurethane onto the paper back of the fiberglass insulation and press it against the metal for several seconds.