Why Insulation Matters
Keeping your home comfortable year-round starts with good insulation. Two of the simplest and most effective ways to save energy (and lower utility bills) are:
- Sealing air leaks around windows, doors, and ducts
- Adding or upgrading insulation in walls, attics, and floors
What Is Insulation?
Simply put, insulation is any material that slows down the flow of heat. It doesn't "create" warmth; instead, it acts like a thermal barrier that keeps heat inside during winter and outside during summer. A blanket doesn't actually create heat (unless it is an electric blanket), but it traps your body heat and keeping you warm. Your home insulation keeps the heat in your home from escaping.
Understanding R-Value: The Key Metric
Insulation is rated using something called an R-Value. The "R" stands for thermal resistance—how well a material resists heat flow.
The Golden Rule:
Higher R-Value = Better insulation
Lower R-Value = Poor insulation
(Note: R-Value is technically measured in units like ft²·°F·h/BTU, but you don't need to memorize the math. Just remember: the number tells you how well the material blocks heat.)
Real-World Example: Windows vs. Walls
- Single-pane window on a cold day: Feels freezing to the touch. Glass has a very low R-Value, so heat escapes easily.
- Interior wall: Feels much warmer. Behind the drywall, there's insulation (like fiberglass or foam) with a higher R-Value, which traps heat inside your living space.
How Layers Work Together
Insulation rarely works alone. In real homes, multiple materials combine to increase the overall R-Value. A typical exterior wall might include:
- Plywood sheathing
- Fiberglass or spray foam insulation
- Drywall
- Exterior siding or brick veneer
Each layer adds its own R-Value. When stacked together, they create a much stronger thermal barrier than any single material could provide on its own.
Look at the table below to learn about six types of insulation.
| Insulation | What is it made of? | What does it look like? | Additional Information |
|---|---|---|---|
Fiberglass
| Molten glass spun into microfibers | Pink or yellow in the form of batts or rolled blankets. | |
Rock Wool
| Basalt Rock (a volcanic stone) and recycled steel slag | Gray or brown fibers in batts or blankets or as shredded loose-fill. | Manufactured in a similar way as fiberglass, but with molten rock instead of glass. |
Cellulose
| Recycled paper – newsprint or cardboard shredded into small bits of fiber. | Blown in as loose fill. | It is treated with fire- and insect-resistant chemicals. |
Rigid Foam
| Different types, but some made from post-consumer recycled content from fast food containers and cups. | Rigid sheets that are applied directly to framing. | Best where space is limited, but a high R-value is needed. Can be installed on the interior of a wall, but if installed inside, must be covered by a fire resistant material like wallboard. One drawback to foam is it deteriorates unless it is protected from prolonged exposure to sunlight and water. It is also more expensive than other insulation. |
Synthetic Insulation
| Usually polystyrene or polyurethane foam. | Polystyrene comes as rigid boards, and Polyurethane comes as rigid boards or sprayed in place systems. | Polystyrene is used for insulating basements, cathedral ceilings, or sidewalls. Polyurethane foams are high performance insulating materials. |
Calculating the Composite R value of a wall, you would just add up all the R values of each layer.
Example
A ceiling is insulated with 0.75" plywood, 2" of polystyrene board, and a 3" layer of fiberglass. What is the R-Value for the ceiling?
Solution:
The ceiling consists of three layers, and all three layers together prevent the heat loss. So, we need to add the R-values of all three layers
¾" of plywood has an R-value of 0.94
2" of polystyrene at 5.0 per inch will have an R-value of 10.00
3" of fiberglass at 3.7 per inch will have an R-value of 11.10
So the R-value of the ceiling is 22.04 ft2 oF h / BTU.
Text description of the Wall Assembly R-Value Breakdown image.
The image illustrates a wall assembly with a focus on the R-Value breakdown, depicting different layers of wall construction and their respective R-Values against a blue background. On the left, a cross-section of a wall is shown with five distinct layers. From the exterior inward, these layers are: brick, wood siding, plywood sheathing, fiberglass insulation, vapor barrier, and drywall. To the right of the wall diagram, each layer is labeled with its material and corresponding R-Value contribution. The R-Values are: wood siding (+R-0.8), plywood sheathing (+R-0.5), fiberglass insulation (+R-11), vapor barrier (+R-0.5), and drywall (+R-0.5). Beneath these, the combined total R-Value is indicated as R-13. At the bottom, a red and orange gradient bar underscores the message: "Better Insulation = Higher R-Value."