1.Fiberglass is a good insulator. Not true.
Fiberglass is a poor insulator. Air is a very good insulator and fiberglass uses the insulation properties of air to make it work. Fiberglass creates millions of tiny air pockets by the way that it is made. Each one of those air pockets is a tiny insulation capsule by itself. But the air must be perfectly still or it can't insulate. The fibers of fiberglass are actually tiny glass strands. That's why they feel so abrasive to our skin and throat. In order for fiberglass to work, it must be installed carefully and fit the space it is in very closely. If it is packed in a space, it loses most of its insulating ability because it is more glass and less air. That's why you can't put 5 ½" (R-19) batts in a 3 ½" (R-13) wall and get the better R-value. You actually get less than R-13 if you do it that way.
2. A long as there is insulation in the wall, it will work as advertised by the printed R value on the paper.
Not True. Fiberglass needs to be installed in a 6 sided wall cavity to work properly. Furthermore, that cavity needs to be air tight. If either of those conditions are not met, the fiberglass will not perform as expected and the R value may be reduced by as much as 50%.
3. Blown fiberglass is the best attic insulation.
Not true. Blown fiberglass has some very serious flaws even before you get to the part about the installer adjusting the blowing equipment. Studies have shown that the colder it gets in the attic, the worse blown fiberglass performs. Meaning that the more you need it, the less effective it is. That's because there is air movement within the blown fiberglass and as some of that air escapes, it takes energy and your hard earned money with it. If an insulation contractor does not adjust the equipment correctly (which is a fine line) the density of the fiberglass will be too low or high. Either way, the insulation value is reduced.
4. Rolling fiberglass insulation out on top of your existing attic insulation will drastically cut heating bills.
Not true. Much of the energy that is being lost from an attic is bypassing the existing insulation. Adding more on top only causes the energy make a zigzag and takes it about an additional second to dissipate. Even if the existing insulation completely fills the cavities it is installed in, there will be pathways for the energy to escape with little resistance.
5. Fiberglass batts with facing are supposed to be stapled to the inside edges of the wood framing in a wall or ceiling.
Not true. The staple tabs should be stapled to the face of the framing. Otherwise there is a channel on each edge that is held open for air to infiltrate and carry energy away before the insulation ever gets a chance to do its job.
6. Fiberglass is better in areas where moisture may be present such as a crawl space.
Not true. Glass is not absorbent so it cannot hold water. When moisture travels through fiberglass insulation, it condenses and water drips out onto wood surfaces and the insulation value drops even further causing more condensation and more water dripping. Mold and rot occur more on wood that is adjacent to fiberglass than would occur if there was no insulation there at all.