Choosing the right insulation is among the most critical decisions in achieving a high-performance, energy-efficient building. With multiple options available—batt, blown-in (loose-fill), and spray foam—understanding each type’s characteristics, pros, and cons is key. In this article, we’ll dissect how each insulation method works and which scenarios favor one over the others.
We’ll cover performance, cost, ease of installation, thermal efficiency, and resilience, to help you make informed decisions tailored to your climate, structure, and goals.
Batt Insulation: Strengths and Weaknesses
Batt insulation (typically fiberglass or mineral wool) comes in pre-cut panels or rolls. It’s a long-established method, fairly easy for DIY or contractor installation in standard stud or joist cavities. Because it’s familiar, many contractors already carry experience, reducing risks in installation.
However, batt insulation’s major weakness is its susceptibility to gaps, compression, and thermal bridging. If not carefully fitted, gaps between batts or at edges weaken performance. Over time, sagging or settling may create voids. Moreover, batts alone do little to stop airflow, so combining them with an air barrier is often necessary to get closer to ideal performance.
Blown-In (Loose-Fill) Insulation
Blown-in (or loose-fill) insulation—often cellulose or fiberglass—is installed via a blowing machine, spraying the material into attic spaces, wall cavities, or irregular areas. It can fill voids and conform to odd shapes better than batts. For retrofit projects, blown-in insulation allows upgrading thermal values without removing drywall.
Its disadvantages include settling over time (especially cellulose) and potential for uneven density or voids if not installed carefully. Also, blown insulation typically does not provide an air-sealing function, so it must be paired with a proper air barrier or sealed sheathing to reduce drafts and moisture infiltration.
Spray Foam: All-in-One Insulation and Air Seal
Spray foam insulation combines thermal insulation and air sealing in one step. As discussed in the first article, it expands to fill gaps and adheres to surfaces. This dual function reduces the need for separate air-sealing layers, making spray foam highly efficient, especially in tight building envelopes or designs that demand minimal energy loss.
Its challenges include higher cost, more complex installation, and the need for trained applicators with proper safety control. In some designs, mechanical ventilation must compensate for significantly reduced natural infiltration (which can reduce fresh-air exchange). But for higher performance homes, spray foam often becomes the top choice.
Performance and R-Value Comparisons
When comparing R-value per inch, closed-cell spray foam generally leads, followed by open-cell foam, then dense-packed cellulose, and finally fiberglass batts in many cases. However, performance isn’t only about R-value; it’s about whole-wall performance including air leakage, thermal bridging, moisture control, and durability.
For example, a wall cavity with batt insulation but leaky framing or sheathing may perform far worse than a thinner layer of spray foam that seals properly. Always evaluate real-world performance—not just stated R-values—when selecting insulation.
Cost vs. Long-Term Value
Batts tend to be lowest cost per square foot, followed by blown-in, and then spray foam. For large, standard cavity areas, batts can be quite economical. Blown-in fills irregular spaces at a moderate cost, while spray foam’s premium reflects its higher performance and labor demands.
Despite higher initial investment, spray foam often yields faster payback in energy savings, especially in climates with extreme temperature swings or in buildings with complex air leakage challenges. Cost also depends on building geometry, access, and existing conditions, so always get detailed estimates and energy modeling.
Best Use Scenarios for Each Type
Batts work well in standard, easy-to-access cavities with regular framing. They’re ideal where budgets are tight and the builder plans to add separate vapor barrier or air barrier layers. Blown-in is excellent for retrofits, filling voids behind walls or in attic spaces with minimal disturbance to existing finishes.
Spray foam is preferred in high-performance construction, passive house designs, or when air sealing is a priority. It’s also the go-to in difficult-to-seal areas like rim joists, cathedral ceilings, or irregular framing geometry. In many cases, hybrid approaches (e.g. spray foam at the envelope + batts in interior cavities) offer compromise solutions.
Installation Tips and Considerations
Regardless of insulation type, proper installation is vital. For batts and blown-in systems, careful attention to fitting, avoiding compression, sealing edges, and avoiding gaps is key. Air barriers, proper ventilation, vapor control layers, and moisture management must also be integrated.
With spray foam, selecting the right density and thickness, ensuring proper spray conditions (temperature, humidity), and post-installation trimming/finishing are important. Additionally, always verify that contractors are certified, refer to manufacturer specs, and ensure that you’re meeting local codes and ventilation requirements.
Conclusion
There is no one-size-fits-all insulation solution. Batt, blown-in, and spray foam each serve different markets, geometries, and budgets. The best choice depends heavily on your building envelope, climate, performance goals, and long-term energy strategy.
At Crown Insulate, we help you assess your project, run energy models, and choose the insulation that balances cost with performance. Contact us to schedule a site audit and get a tailored proposal that fits your needs.
