Although you need to rent equipment for blowing in loose fill, the convenience makes it worthwhile, especially if the alternative is crawling around in a low attic for one or two days.

Suitability. Consider the nature of the space to be insulated. If it is open framing, use blankets or batts. If the framing members are not spaced regularly, for a ceiling or unfinished floor, pour loose fill between them. If it is a cavity enclosed by finished walls and ceilings, you will have to use blown fill. On the outside surface of a wall or roof, use rigid panels.

Dimension. Rigid panels give the most R-value per inch, making them ideal for tight spaces or where additional wall thickness must be kept to a minimum. If you have 2 by 4 stud walls and want to insulate to R-19, you need more than batts, blankets, or blown fill between the studs. Use rigid panels or fill the stud cavities with low-R material and add thin rigid panels under the wallboard or siding.

Which type of insulating material is best for your project? All things being equal, you want to know what has the highest R-value. However, since all things are never equal, there are other factors you should consider.

Convenience. When doing the work yourself, choose the material that is easiest to install. That usually means fiberglass blankets or batts, since they are readily available and do not require specialized tools to install. rockwool blankets have a slightly higher R-value, but are not as easy to find.

Flammability. When installing rigid panels between the exposed rafters of a sloped ceiling, you must either cover the panels with wallboard, or use fiberglass panels. Any type of cellulose insulation must be treated with a fire retardant.

Moisture Resistance. Some types of loose insulation, such as cellulose, compact together and become useless when wet. This is no problem if walls are properly sealed and protected with a vapor barrier, but may be a factor in regions that get periodic flooding or high humidity.

The most durable insulating material is extruded polystyrene (at this writing), which can even be submerged.