Attic insulation plays a major role in keeping your home comfortable and your energy bills manageable. It slows the transfer of heat between the living space and the outdoors, reducing the workload on your heating and cooling systems. But with several types of attic insulation available, it can be difficult to know which one is right for your home. This guide compares the most common options—fiberglass, cellulose, mineral wool, spray foam, rigid foam board, and reflective insulation—so you can make an informed decision.
Why the Type of Attic Insulation Matters
Not all insulation performs the same way. Each material has a different R-value (a measure of thermal resistance), installation method, and cost. The right choice depends on your climate, attic structure, budget, and whether you plan to install it yourself or hire a professional. Understanding these differences helps you avoid common mistakes and get the best performance for your money.
Key Factors to Compare
- R-value: The higher the R-value, the better the insulation resists heat flow. Recommended levels vary by climate and building codes.
- Material: Some materials are better at sealing air leaks, while others excel at fire resistance or moisture control.
- Installation method: Options include batts, loose-fill, spray foam, and rigid panels. Some are DIY-friendly; others require a professional.
- Cost: Upfront prices range from inexpensive fiberglass to premium spray foam. Consider long-term energy savings as well.
- Durability and lifespan: Most insulation lasts for decades, but some materials settle, absorb moisture, or degrade if not installed correctly.
- Moisture and fire resistance: Fire ratings and moisture behavior matter, especially in humid or fire-prone areas.
Common Types of Attic Insulation
1. Fiberglass Insulation
Fiberglass is one of the most widely used insulation materials. It is made from fine glass fibers and is available in two main forms: batts and blankets (pre-cut rolls) and loose-fill (blown-in).
Pros: Affordable, widely available, easy to install in standard joist spaces, and resistant to fire and moisture when properly installed.
Cons: Can irritate skin, eyes, and lungs during installation, so protective gear is essential. It may lose effectiveness if compressed or if air leaks are not sealed first.
2. Cellulose Insulation
Cellulose is made from recycled paper products, such as newspaper, treated with fire retardants. It is typically installed as loose-fill, either blown dry or sprayed damp.
Pros: Eco-friendly, good at filling irregular spaces and gaps, and generally has a higher R-value per inch than fiberglass. It also dampens sound.
Cons: Can settle over time, reducing its R-value. It absorbs moisture, so proper ventilation and moisture control are important. Installation can be dusty.
3. Mineral Wool Insulation
Mineral wool, also known as rock wool or slag wool, is made from molten rock or industrial waste. It comes in batts and loose-fill form.
Pros: Excellent fire resistance, water repellent, and effective at blocking sound. It maintains its R-value even when compressed.
Cons: More expensive than fiberglass or cellulose. It is heavier and may require professional installation for best results.
4. Spray Foam Insulation
Spray foam is a two-part liquid that expands into a foam, sealing gaps and creating an airtight barrier. It comes in two types: open-cell and closed-cell.
Open-Cell Spray Foam
Open-cell foam is lighter, less dense, and expands more. It has a lower R-value per inch but is good for interior applications where airtightness is key.
Closed-Cell Spray Foam
Closed-cell foam is denser, stronger, and has a higher R-value per inch. It also acts as a vapor barrier and can add structural rigidity.
Pros: Excellent air sealing, high R-value (especially closed-cell), and effective at filling hard-to-reach areas.
Cons: More expensive than traditional materials. Professional installation is usually required. Some foams may release odors during curing.
5. Rigid Foam Board Insulation
Rigid foam board is made from materials like polystyrene, polyisocyanurate, or polyurethane. It comes in large panels.
Pros: High R-value per inch, moisture resistant, and easy to cut and fit. Often used in attics with limited space.
Cons: More expensive than fiberglass or cellulose. Requires careful sealing of seams to prevent air leaks. Can be flammable and may need a fire barrier.
6. Reflective Insulation (Radiant Barriers)
Reflective insulation, often called a radiant barrier, is made of a shiny reflective material, such as aluminum foil, backed by paper or plastic. It works by reflecting radiant heat rather than absorbing it.
Pros: Effective at reducing heat gain in hot climates. Thin and easy to install in tight spaces.
Cons: Does not provide a high R-value on its own; it works best when combined with other insulation. Performance depends on proper installation with an air space facing the reflective side.
Comparison at a Glance
| Type | Common Forms | Approx. R-Value per Inch | Best For |
|---|---|---|---|
| Fiberglass | Batts, loose-fill | 2.2-2.7 | Standard attics with regular joist spacing |
| Cellulose | Loose-fill | 3.1-3.7 | Irregular spaces, eco-friendly projects |
| Mineral Wool | Batts, loose-fill | 3.0-3.3 | Fire resistance, soundproofing |
| Open-Cell Spray Foam | Sprayed | 3.6-3.9 | Airtight sealing, interior walls |
| Closed-Cell Spray Foam | Sprayed | 6.0-6.5 | High R-value, vapor barrier, structural |
| Rigid Foam Board | Panels | 4.0-6.0 | Limited space, exterior walls, attic hatches |
| Reflective Insulation | Foil sheets | N/A (depends on air space) | Hot climates, radiant heat control |
How to Choose the Right Attic Insulation
- Climate: In cold climates, focus on high R-value and air sealing. In hot climates, reflective insulation or closed-cell foam can help with radiant heat.
- Existing insulation: If you already have some insulation, you may be able to add more of the same type or choose a compatible material.
- Attic type: Vented attics often use loose-fill or batts, while unvented attics (sealed attics) are better suited for spray foam.
- Budget: Fiberglass and cellulose are generally the most affordable. Spray foam and rigid board are more expensive upfront but may offer better performance.
- DIY vs. professional installation: Some materials, like batts and loose-fill, can be DIY projects. Spray foam and some rigid board applications are best left to professionals.
Installation Tips and Safety
- Always seal air leaks (around pipes, wires, and gaps) before adding insulation. Insulation works best when air leakage is controlled.
- Wear protective clothing, gloves, goggles, and a respirator when handling insulation materials.
- Ensure proper ventilation in the attic to prevent moisture buildup, especially with cellulose and open-cell foam.
- Do not block soffit vents or other ventilation openings. Use baffles to keep air flowing.
- Check local building codes for requirements on R-values, fire barriers, and vapor barriers.
Conclusion
Attic insulation is not a one-size-fits-all solution. The best type for your home depends on your climate, attic structure, budget, and installation preferences. Fiberglass and cellulose are affordable and widely available, mineral wool offers fire and sound resistance, spray foam provides superior air sealing, rigid foam board is great for tight spaces, and reflective insulation helps with radiant heat. By comparing these options and considering your specific needs, you can choose an insulation that improves comfort and lowers energy costs.
For more practical home improvement and energy-saving guides, explore our other articles on topics like air sealing, attic ventilation, and DIY repairs.