Choosing the right insulation material is one of the most consequential decisions a homeowner can make. Each type has unique properties that make it suited for different applications, budgets, and performance requirements. The material that works best for an attic floor upgrade is often the wrong choice for a basement rim joist, and the ideal product for a tight cathedral ceiling cavity differs from what belongs in an exterior wall.
This guide covers every major residential insulation material with the data you need to make an informed decision.
R-Value Comparison by Material
Before diving into the details, here is how all major insulation materials compare at a glance:
| Insulation Material | R-Value Per Inch | Creates Air Barrier? | Best Applications | |---------------------|-----------------|----------------------|-------------------| | Closed-Cell Spray Foam | R-6.0 to R-7.0 | Yes | Walls, crawl spaces, rim joists, roofs | | Polyisocyanurate Board | R-5.6 to R-8.0 | Yes | Roof decks, wall sheathing, continuous insulation | | Extruded Polystyrene (XPS) | R-5.0 | Yes | Below-grade, foundations, under slabs | | Expanded Polystyrene (EPS) | R-3.6 to R-4.2 | Yes | Walls, roofs, below-grade | | Open-Cell Spray Foam | R-3.5 to R-3.9 | Yes | Interior walls, attics, soundproofing | | Blown-In Cellulose | R-3.1 to R-3.8 | No | Attics, wall cavities | | Mineral Wool / Rockwool | R-3.1 to R-3.4 | No | Walls, fire-rated assemblies | | Fiberglass Batts | R-2.9 to R-3.8 | No | Walls, attics, floors | | Blown-In Fiberglass | R-2.2 to R-2.9 | No | Attics, hard-to-reach spaces |
Fiberglass Insulation
Fiberglass is the most common insulation type in American homes. It is made from melted recycled glass and sand spun into fine fibers, and comes in two primary forms.
Fiberglass Batts and Rolls are pre-cut panels designed to fit between standard wall studs, floor joists, and attic rafters. They offer R-2.9 to R-3.8 per inch and are the familiar pink or yellow rolls found in most home improvement stores.
- Pros: Affordable, widely available, naturally non-combustible, moisture resistant, no specialized equipment required
- Cons: Can leave significant gaps if not installed precisely, does not create an air barrier, loses effectiveness if compressed or wet, irritating during handling
Blown-In Fiberglass provides R-2.2 to R-2.7 per inch and covers irregular spaces better than batts because the loose material flows around wiring, pipes, and other obstacles.
- Pros: Better coverage in irregular spaces, fireproof, minimal settling over time
- Cons: Lower R-value per inch than cellulose, requires blowing equipment, can shift in attics with significant air movement
Cellulose Insulation
Cellulose is composed primarily of recycled paper -- mostly ground-up newspaper -- treated with fire retardants like borates. It is almost exclusively installed as blown-in insulation and has grown in popularity due to its environmental profile and strong thermal performance.
Cellulose achieves R-3.1 to R-3.8 per inch, notably higher than blown-in fiberglass. This means it reaches the same R-value in less depth, which matters in spaces where available headroom is limited.
- Pros: Higher R-value per inch than fiberglass, excellent gap-filling that reduces air infiltration, made from up to 85% recycled materials, treated with borates for fire and pest resistance
- Cons: Can absorb moisture if not properly protected, may settle 15-20% over time, heavier than fiberglass
- Cost: Typically $0.60 to $2.30 per square foot installed
In 2x6 wall cavities, cellulose stops air 35% better than fiberglass, which translates directly into reduced drafts and improved year-round comfort across Northern Virginia homes.
Spray Foam Insulation
Spray foam is a two-part liquid polyurethane mixture that expands into dense foam when applied, filling cracks, gaps, and cavities to create both an air barrier and an insulating layer simultaneously. Spray foam actively seals while it insulates, eliminating the gaps that allow air infiltration regardless of insulation depth.
Open-Cell Spray Foam is light and spongy with an R-value of R-3.5 to R-4.0 per inch. It is less expensive than closed-cell and allows some breathability, making it well-suited for interior walls and soundproofing applications.
Closed-Cell Spray Foam is dense and rigid with an R-value of R-6.0 to R-7.0 per inch -- among the highest available for any residential insulation material. It also functions as a moisture barrier and adds structural rigidity. Closed-cell is the preferred choice for exterior walls, basements, crawl spaces, and roofs where both insulation and moisture control are critical.
| Feature | Open-Cell | Closed-Cell | |---------|-----------|-------------| | R-Value Per Inch | R-3.5 to R-4.0 | R-6.0 to R-7.0 | | Moisture Barrier | No | Yes | | Structural Support | Minimal | Yes | | Cost Per Board Foot | $0.44-$0.65 | $0.90-$1.50 | | Typical Lifespan | 50+ years | 50+ years |
DOE research shows spray foam can reduce air infiltration by up to 40% more than traditional insulation. Average total project costs range from $3,500 to $12,000 depending on area and complexity.
Mineral Wool (Rockwool) Insulation
Mineral wool is made from natural minerals like basalt melted at extremely high temperatures and spun into fibers. It provides R-3.1 to R-3.4 per inch -- comparable to fiberglass batts -- but stands out in three critical areas.
Fire Resistance: Mineral wool is non-combustible and withstands temperatures above 1,000 degrees C (1,832 degrees F). It does not burn, does not produce smoke, and does not promote flame spread, making it the standard choice for fire-rated wall assemblies.
Soundproofing: Its dense fiber structure effectively dampens sound waves, reducing noise transmission between rooms and from external sources better than any other batt-format insulation.
Moisture Resistance: Mineral wool is hydrophobic -- it repels water rather than absorbing it -- and will not support mold or bacteria growth even in damp conditions.
- Pros: Exceptional fire resistance, excellent soundproofing, water-repellent, dense friction fit stays in place
- Cons: Higher cost than fiberglass, heavier to handle, limited blown-in availability
- Cost: Approximately $4-$5 per square foot installed
Rigid Foam Board Insulation
Rigid foam boards come in three main types and provide a continuous insulation layer that addresses thermal bridging through studs and framing -- one of the key weaknesses of cavity-only insulation strategies.
Expanded Polystyrene (EPS): R-3.6 to R-4.2 per inch. The most affordable rigid foam option, with excellent moisture resistance suited for below-grade applications like foundation walls and under-slab insulation.
Extruded Polystyrene (XPS): R-5.0 per inch. The familiar blue, green, or pink boards widely used for wall and below-grade applications. Strong moisture resistance, though R-value may slowly decline over decades due to thermal drift.
Polyisocyanurate (Polyiso): R-5.6 to R-8.0 per inch -- the highest per inch of any rigid board. Excellent for roof decks and continuous wall sheathing, though effective R-value can decrease at very low temperatures, a consideration for Northern Virginia winters.
Choosing the Right Material for Your Project
No single insulation material is best for every application. For attic floor upgrades in Northern Virginia homes, blown-in cellulose or blown-in fiberglass are the most practical and cost-effective choices -- they cover existing insulation uniformly, fill around obstacles, and reach R-49 to R-60 efficiently. For rim joists and crawl spaces, closed-cell spray foam provides the best combination of high R-value per inch, air sealing, and moisture resistance. For exterior continuous insulation, rigid foam board addresses thermal bridging that cavity insulation alone cannot resolve.
EcoGuard Insulation works with homeowners across Northern Virginia -- from Reston and Herndon to Woodbridge and Warrenton -- to select and install the right insulation material for each specific application. Contact us for a free assessment and recommendation tailored to your home.