Good insulation lowers energy bills by trapping heat or cold air inside a building. While fiberglass insulation is easier to install and more common (used about 85% of the time), cellulose insulation is often considered more energy efficient.
Comparison chart
 | Cellulose Insulation | Fiberglass Insulation |
|---|---|---|
 |  | |
| How it works | Cellulose cells have natural insulating power. | Traps air inside tiny glass fibers, slowing transfer of heat. |
| Cost | Around $0.40 per square foot | Around $0.40 per square foot |
| Air leakage | Less | Yes |
| Installation | Fibers blown into gap in wall. | Sheets placed in wall |
| Energy efficiency | More efficient | Less efficient |
| Flammability | No, as heavily treated with boric acid | Potentially, due to kraft paper on batts. |
| Extreme cold | No difference | Loses heat quickly |
How it works
Cellulose insulation includes cellulose cells that have natural insulating power. It is made of shredded paper plus a fire retardant chemical known as a borate. The paper is broken down into cellular fibers that provide insulation.
Fiberglass insulation contains billions of tiny glass fibers, which contain trapped bubbles of air. These air bubbles slow the transfer of heat.
Pros and Cons
Fiberglass insulation is more common and can be installed more easily. However, it does not prevent air leakage and is potentially flammable. Fiberglass insulation loses heat quickly in extreme low temperatures.
Advantages of cellulose insulation include
- a high R-value i.e. higher energy efficiency, and
- better sound insulation.
The disadvantages of cellulose include:
- More expensive and requires professional installation
- City and regional/state building codes may not be updated for cellulose insulation
- Dust: Blown cellulose is prone to create dust that is blown into the house through minute holes or inadequate seals around fixtures. This is a health hazard.
- Removal of cellulose insulation is costly.
- Weight: Cellulose insulation weighs more than fiberglass for the same R-value. So building structures should be inspected for signs of weakness before choosing the insulation material.
- Drying time for wet-spray: Wet-spray is used for better sealing but takes a very long time to dry. Drywall or sheet-rock cannot be applied to a newly insulated wall until then.
In this video, a home inspector from central Texas gives his opinion and carefully compares the two types of insulation. It is slow but worth watching.
On the other hand, the following video is opinionated and argues in favor of cellulose insulation:
Energy efficiency
Cellulose insulation, like spray foam insulation, limits air movement. A study by the University of Colorado found that cellulose insulation reduced air leakage by 38%.
Fiberglass insulation cannot stop air from passing through it, meaning that more than 30% of heat or air conditioning can escape.
R value
A product’s r-value is its resistance to heat flow. A higher R-value prevents more heat from escaping through the insulation. Homes generally require insulation with an R-value of around 38. The R-value of cellulose insulation is approximately 3.8 per inch so you need about insulation that is about 10 inches thick to reach R-38. The R-value of fiberglass insulation is approximately 2.2 per inch so you need much thicker insulation to achieve the same R-value of 38.
Cost
Both cellulose insulation and fiberglass insulation are low-cost and have a similar inch-for-inch price. However, as cellulose insulation often requires professional installation and specialized skills, it usually turns out to be more expensive.
Installation Process
Cellulose insulation is installed using an insulation blower. The fibers flow through a long hose and are blown or sprayed into the space. The machine can densely pack the fibers, creating an even layer of insulation that fills all gaps. It is usually installed by a professional.
Fiberglass insulation usually comes in batts or rolls. In order to be completely effective, fiberglass insulation must be cut carefully around obstacles such as power sockets. This can be incredibly time consuming. If an individual is willing to settle a less effective job, fiberglass can be easily installed without professional assistance.
Here's an informative video about overcoming 3 main problems in installing a fiber glass insulation.
Fiberglass Insulation 
Metal Roof 
Electric Heating 
Joist 
Laminate 
Drywall
Comments: Cellulose Insulation vs Fiberglass Insulation