Your attic is where the biggest chunk of a home’s heating and cooling dollars escapes. Adding or upgrading insulation is one of the highest-return home improvements you can make, often paying for itself in a few years of lower energy bills. But the shelves are full of choices, and picking the wrong one wastes money. This guide breaks down the main types of attic insulation, their R-values, costs, and the situations each one suits best, so you can insulate smart the first time.
Understanding R-Value First
Every insulation material is rated by its R-value, a measure of resistance to heat flow. The higher the R-value, the better it insulates. What matters in an attic is the total R-value across the whole floor, which comes from the material’s per-inch rating multiplied by its thickness.
The U.S. Department of Energy recommends attic insulation of roughly R-38 to R-60 for most of the country, which translates to about 13 to 20 inches of material depending on the type. Southern climates aim for the lower end, northern climates the higher end. Knowing your target R-value tells you how much of any given material you need.
Fiberglass: The Everyday Standard
Fiberglass is the most common attic insulation, sold as batts (pre-cut rolls) or loose-fill (blown in). It is made from spun glass fibers and offers about R-2.2 to R-4.3 per inch.
Pros:
- Inexpensive, roughly $0.30 to $1.50 per square foot for materials.
- Non-combustible and does not absorb water readily.
- DIY-friendly, especially batts between standard joist spacing.
Cons:
- Batts leave gaps if not cut precisely, reducing performance.
- Loses some R-value in extreme cold unless properly installed.
- Irritates skin and lungs, so gear up during installation.
Blown-in fiberglass is excellent for topping up an existing attic because it flows into odd cavities and around obstructions that batts cannot fill neatly.
Cellulose: The Eco-Friendly Blown-In
Cellulose is made from recycled paper (mostly newsprint) treated with borate for fire and pest resistance. It is almost always blown in and delivers about R-3.2 to R-3.8 per inch.
Pros:
- High recycled content, appealing for green-minded homeowners.
- Dense pack fills gaps well and reduces air movement.
- Costs around $0.60 to $2.00 per square foot installed.
- Borate treatment resists insects and rodents.
Cons:
- Heavier than fiberglass, so confirm the ceiling can bear the load.
- Can settle over time, losing a bit of thickness and R-value.
- Absorbs moisture more than fiberglass, so leaks must be fixed first.
Spray Foam: The High-Performance Air Seal
Spray polyurethane foam is applied wet and expands to fill every crack, sealing air leaks as it insulates. It comes in two forms:
- Open-cell foam: softer, about R-3.5 to R-3.9 per inch, less expensive.
- Closed-cell foam: dense and rigid, about R-6 to R-7 per inch, also a moisture barrier.
Pros:
- Highest R-value per inch and unmatched air sealing.
- Closed-cell adds structural rigidity and blocks moisture.
- Does not settle or sag over time.
Cons:
- Expensive, typically $1.50 to $4.50 per square foot installed.
- Professional installation strongly recommended for large areas.
- Requires careful ventilation planning to avoid trapping moisture.
Spray foam is often applied to the underside of the roof deck to create a conditioned, or “hot roof,” attic, useful when HVAC equipment lives in the attic.
Mineral Wool and Rigid Foam Board
Mineral wool (rock wool) is spun from stone or slag, offering about R-3 to R-3.3 per inch. It is fire-resistant, water-repellent, and excellent at sound dampening, though it costs more than fiberglass at roughly $1.00 to $2.50 per square foot.
Rigid foam board (EPS, XPS, or polyiso) delivers R-4 to R-6.5 per inch in stiff panels. It is less common on attic floors but valuable for insulating attic hatches, knee walls, and rafters where a thin, high-R material helps.
How to Choose the Right Type
Match the material to your goal and budget:
- Best value for topping up an attic: blown-in fiberglass or cellulose.
- Best DIY for a bare, accessible attic: fiberglass batts.
- Best air sealing and performance: spray foam, especially in complex or humid attics.
- Best fire and sound resistance: mineral wool.
- Best for tight spots and hatches: rigid foam board.
Before adding any insulation, air-seal the attic floor: caulk and foam around penetrations, seal the attic hatch, and ensure soffit vents are not blocked. Insulation works far better over a sealed, ventilated ceiling. A blower-door test from an energy auditor can reveal exactly where you are losing air.
Installation Methods and What They Cost to Do
Beyond the material itself, how insulation gets installed affects both cost and performance. Understanding the methods helps you plan the project:
- Batts (DIY-friendly): Pre-cut rolls laid between joists. Best for accessible attics with standard joist spacing and few obstructions. A confident homeowner can insulate a small attic in a weekend for the cost of materials alone, roughly $0.30 to $1.50 per square foot.
- Blown-in (loose-fill): A machine blows fiberglass or cellulose to an even depth. Many home centers lend or rent the blower free with a bulk purchase, making DIY blown-in realistic. Professional blown-in installation runs about $1 to $2.50 per square foot installed.
- Spray foam (professional): Requires specialized equipment and safety gear, so it is almost always contractor-installed. Expect $1.50 to $4.50 per square foot depending on open- or closed-cell and thickness.
A practical middle path many homeowners choose is to lay batts or top up with blown-in themselves while hiring a pro for air sealing or spray foam in tricky spots. Before you insulate, always address ventilation and air leaks. Baffles at the eaves keep soffit vents clear so airflow is not blocked, and sealing gaps around chimneys, plumbing stacks, wiring, and the attic hatch prevents warm, moist air from rising into the cold attic where it can condense. Insulation laid over a leaky, poorly ventilated attic underperforms and can even trap moisture, so these preparatory steps are as important as the R-value you install. A blower-door test and a quick infrared scan from an energy auditor, often $200 to $500, pinpoint exactly where your home leaks heat.
Frequently Asked Questions
What is the best type of attic insulation? There is no single winner. For most homes topping up existing insulation, blown-in cellulose or fiberglass offers the best cost-to-performance ratio. For maximum air sealing and R-value, closed-cell spray foam leads but costs the most.
Can I put new insulation over old? Usually yes. You can add blown-in insulation or unfaced batts on top of existing material, as long as the old insulation is dry and not moldy. Never add a second layer of faced (paper-backed) batts, as the vapor barrier can trap moisture.
How much insulation do I need? Aim for R-38 to R-60 total, roughly 13 to 20 inches depending on the material. Southern homes target the lower end and northern homes the higher end.
Is spray foam worth the extra cost? If you have persistent air leaks, an unconditioned attic housing HVAC equipment, or a moisture problem, closed-cell spray foam’s sealing and R-value can justify the price. For a simple top-up, cheaper blown-in options usually make more financial sense.
How much does it cost to insulate an attic? For an average home, adding blown-in fiberglass or cellulose typically runs $1,500 to $3,500 installed, while a full spray foam job can reach $4,000 to $8,000 or more. DIY batts or blown-in can cut that substantially, often to a few hundred dollars in materials for a small attic. Utility rebates and federal energy tax credits can offset part of the cost, so check what incentives apply in your area before you start.
Which insulation is best for hot climates? In hot regions, pair adequate attic-floor insulation with a radiant barrier to block summer heat gain. Blown-in cellulose or fiberglass at the recommended R-value handles the conductive load, and the radiant barrier reflects the sun’s radiant heat before it reaches your ceiling.
Choosing among the types of attic insulation comes down to your climate, your budget, and whether you need simple thermal resistance or serious air sealing. Hit your target R-value, seal the attic floor first, and you will enjoy a more comfortable home and noticeably lower energy bills for decades.
