If you’re a homeowner in San Diego County looking to upgrade your attic insulation, you’ve likely come across two of the most common materials on the market: cellulose and fiberglass insulation. While both are widely used in residential construction and retrofits, they have key differences in performance, material composition, installation method, and environmental impact.
So which one is better for your home?
In this comprehensive guide, we’ll walk you through everything you need to know about cellulose insulation vs fiberglass insulation, so you can make the smartest choice for your attic, your energy bill, and your long-term comfort.
What Is Cellulose Insulation?
Cellulose insulation is made from recycled paper products—mostly old newspapers—which are shredded and treated with a fire retardant such as boric acid. The result is a dense, eco-friendly, fire-resistant loose-fill material that can be blown into attics or dense-packed into walls.
Key Benefits of Cellulose Insulation:
- Made from 85% recycled materials
- Treated to be fire-, pest-, and mold-resistant
- Blown-in application fills hard-to-reach gaps
- Provides excellent soundproofing
- Higher R-value per inch than most fiberglass products
What Is Fiberglass Insulation?
Fiberglass insulation is made by spinning molten glass into thin fibers and forming it into batts (rolls) or loose-fill particles for blown-in applications. It’s one of the most common types of insulation in the U.S. due to its wide availability, affordability, and fire resistance.
Key Benefits of Fiberglass Insulation:
- Made from glass and sand, often with recycled content
- Naturally non-combustible
- Resists moisture and mold
- Available in both batts and blown-in forms
- Typically cheaper than cellulose
Head-to-Head: Cellulose Insulation vs Fiberglass Insulation
| Feature | Cellulose Insulation | Fiberglass Insulation |
|---|---|---|
| Material | Recycled paper (mostly newspaper) | Spun glass fibers |
| R-Value per inch | 3.2 – 3.8 | 2.2 – 2.7 (batts), 2.9 – 3.2 (blown-in) |
| Soundproofing | Excellent | Good |
| Fire Resistance | Good (treated with borates) | Excellent (naturally non-combustible) |
| Moisture Resistance | Fair (can absorb water) | Excellent (non-absorbent) |
| Pest Resistance | Treated to resist rodents & insects | Naturally pest-resistant |
| Settling Over Time | Yes (can settle 20% or more) | Minimal |
| Installation Method | Blown-in only | Blown-in or batt |
| Environmental Impact | Very eco-friendly (up to 85% recycled content) | Less eco-friendly (20–40% recycled) |
| Cost | Moderate to high | Generally more affordable |
| Lifespan | 20–30 years | 30+ years (if undisturbed) |
Which Insulation Performs Better in San Diego County?
San Diego’s mild coastal climate combined with hot inland summers makes energy efficiency a top priority for homeowners. Here’s how cellulose and fiberglass perform in real-life San Diego homes:
✅ Energy Efficiency
If your goal is maximum energy savings, cellulose has a slight edge due to its higher R-value per inch. This means less material is needed to achieve the same level of thermal resistance.
✅ Air Sealing and Coverage
Blown-in cellulose is denser and settles better into tight cavities and gaps, making it an excellent air barrier—ideal for older homes with uneven or hard-to-reach spaces in the attic.
✅ Rodent Resistance
Fiberglass doesn’t offer food or nesting material for rodents, while cellulose is treated to repel pests. In areas prone to rodent activity, either material can be effective, but proper rodent proofing is more important than insulation type.
✅ Fire Safety
Fiberglass is naturally non-flammable, making it a better option if fire resistance is your top concern. However, cellulose that’s treated with borates also meets fire safety standards.
✅ Moisture and Mold
Fiberglass resists moisture and does not support mold growth, which can be useful in coastal areas of San Diego where humidity levels rise. Cellulose can absorb moisture, making vapor barriers or professional installation crucial.
Environmental Considerations
Both insulation types have environmental pros and cons:
- Cellulose is made from post-consumer waste, which reduces landfill usage and carbon footprint. It’s the most eco-friendly insulation option available today.
- Fiberglass uses less recycled content overall but has improved significantly in recent years. Many brands now offer formaldehyde-free fiberglass with better sustainability profiles.
Installation Process: What to Expect
At Attic Shield, we offer both fiberglass and cellulose insulation installation. Here’s what the process typically involves:
Cellulose Insulation Installation:
- Remove existing insulation (if necessary)
- Seal air leaks and entry points
- Sanitize attic space
- Blow in dense-pack cellulose to recommended R-value
- Clean up and take post-job photos
Fiberglass Insulation Installation:
- For batt insulation: roll-out and staple method between rafters
- For blown-in fiberglass: similar process as cellulose with different blower settings
Both options take 1 day or less to complete for most San Diego homes.
Pros and Cons Summary
✅ Cellulose Insulation Pros:
- High R-value per inch
- Great air sealing and soundproofing
- Eco-friendly
- Ideal for tight and irregular spaces
❌ Cellulose Cons:
- Can settle over time
- May absorb moisture
- Requires careful professional installation
✅ Fiberglass Insulation Pros:
- Fireproof and moisture-resistant
- Long lifespan
- More budget-friendly
- Readily available
❌ Fiberglass Cons:
- Lower R-value per inch
- Gaps can occur with batt installation
- Less eco-friendly
Our Recommendation: Which Should You Choose?
If your home has a tight attic space, is older, or suffers from heat retention in the summer, blown-in cellulose offers superior coverage and comfort. For newer homes or remodels on a budget, fiberglass is a perfectly suitable, cost-effective choice—especially if rodent issues or moisture are a concern.
At Attic Shield, we help homeowners in San Diego, Temecula, and Lake Elsinore choose the right insulation material based on their attic structure, home layout, and energy goals. We never push one solution for every home. Instead, we focus on what will deliver long-term value, efficiency, and peace of mind.
Why Homeowners Choose Attic Shield
- ✔ Licensed C-2 Insulation Contractor
- ✔ Free attic inspections with photo documentation
- ✔ Professional insulation removal and cleanup
- ✔ Full attic sanitization and rodent-proofing
- ✔ Same-day or next-day service
- ✔ Financing options available
- ✔ Serving all of San Diego County and surrounding areas
Request Your Free Estimate Today
Still unsure whether cellulose or fiberglass is right for your attic? Let us help you decide. Schedule a free attic evaluation with our team and we’ll walk you through every option—showing you photos, R-value recommendations, and exact pricing.
📞 Call now: 858-402-0066
Final Thoughts
The debate between cellulose insulation vs fiberglass insulation doesn’t have a one-size-fits-all winner. Both options offer unique strengths—and when installed by a trusted professional like Attic Shield, you can’t go wrong.
The key is selecting the right material for your home’s structure, budget, and long-term comfort goals.
Let’s create an attic that works for you—not against you.
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