When selecting insulation for a home, R-value is the primary metric for thermal performance. This article compares three common materials: fiberglass, mineral wool, and cellulose, focusing on their R-values per inch and overall effectiveness.
Fiberglass Insulation
Fiberglass, made from spun glass fibers, offers an R-value of approximately 2.9 to 3.8 per inch. Its lightweight nature makes it easy to install in batts or loose-fill forms. However, its performance can degrade if compressed or if air leaks occur, since it does not block airflow as effectively as denser materials. In colder climates, fiberglass may require thicker layers to meet building codes.
Mineral Wool Insulation
Mineral wool, also known as rock wool or slag wool, provides an R-value of 3.3 to 4.2 per inch. It is denser than fiberglass, which helps reduce air movement and improves soundproofing. Mineral wool is naturally fire-resistant and water-repellent, maintaining its insulating properties even in humid conditions. Its higher density means it can achieve better thermal performance with less thickness, making it suitable for tight spaces.
Cellulose Insulation
Cellulose, made from recycled paper treated with fire retardants, boasts an R-value of 3.5 to 3.8 per inch. Its dense, loose-fill form allows it to settle into cavities, effectively blocking air infiltration. Research shows cellulose can reduce air leakage by up to 30% compared to fiberglass. However, its R-value may decrease slightly over time due to settling, though proper installation mitigates this. Cellulose is an eco-friendly choice with strong overall thermal performance.
Choosing the Best Option
For budget-conscious projects, fiberglass remains a cost-effective standard. For fire safety and sound control, mineral wool excels. For superior air sealing and sustainability, cellulose is ideal. Ultimately, the best choice depends on your climate, installation requirements, and long-term energy goals. Proper installation is critical for all materials to achieve their rated R-values.