Rockwool vs. Fiberglass

Comparing Insulation: Rockwool vs. Fiberglass

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Insulation is a critical component of any building, affecting energy efficiency, comfort, and even the health of occupants. When selecting insulation materials, you’re faced with a number of choices, each with its own set of properties and performance characteristics. Two of the most commonly used materials for insulation are rockwool and fiberglass. Each has its advantages and disadvantages, which can influence your decision depending on your specific needs and conditions.

Rockwool, also known as mineral wool, is made from natural basalt rock and recycled slag. It’s recognized for its fire resistance, sound absorbency, and durability. Additionally, it does not easily absorb water, making it less susceptible to mold and mildew growth, a plus for indoor air quality. On the other hand, fiberglass is created from fine strands of glass and is widely used due to its cost-effectiveness and ease of installation. Its lightweight nature and versatility make it a popular choice for many, but it can be less effective if not properly installed, and its tiny fibers can be a concern for indoor air quality if they become airborne.

Understanding the differences between rockwool and fiberglass insulation is essential to making an informed choice when insulating your home or building. You must consider factors such as thermal performance, sound insulation, environmental impact, and cost. This comparison will offer you the insight needed to determine which type of insulation aligns best with your specific requirements and goals for energy efficiency and comfort.

Fundamental Properties

When comparing rockwool and fiberglass insulation, it’s essential to understand their fundamental properties. These properties include material composition, thermal performance, sound insulation, and fire resistance, which influence the suitability of each material for specific applications.

Material Composition

Rockwool, also known as mineral wool, is made from natural basalt rock and recycled slag. Basalt, a volcanic rock, is melted and spun into fine fibers to create the insulation. Fiberglass, on the other hand, is fabricated from a mixture of fine fibers of glass. Both materials contain a binder to hold the fibers together.

Thermal Performance

The thermal performance of insulation is measured by its R-value, which reflects its resistance to heat flow. Fiberglass typically has an R-value between R-2.9 to R-3.8 per inch of thickness. Rockwool has a slightly higher R-value, ranging from R-3 to R-3.3 per inch. This indicates that rockwool can offer superior insulation per inch compared to fiberglass.

Sound Insulation

Both rockwool and fiberglass help in reducing sound transmission but do so with different efficacies. Rockwool possesses a denser structure, which tends to absorb and block sound more effectively than fiberglass. Fiberglass still provides adequate sound dampening, especially in higher densities, but may not match the sound insulation capabilities of rockwool.

Fire Resistance

Fire resistance is a crucial factor in insulation materials. Rockwool is non-combustible and can withstand temperatures above 1000°C without melting. Fiberglass is also non-combustible but has a lower melting point than rockwool. This makes rockwool a preferable choice in scenarios where higher fire resistance is demanded.

Installation and Application

When choosing insulation for your home, understanding how rockwool and fiberglass are installed and their effectiveness in different climates can influence your decision.

Ease of Installation

You’ll find that fiberglass insulation is lighter than rockwool, which often makes it easier to handle and install. It’s available in batts and rolls that can be cut to fit various spaces using a simple utility knife. However, you need to wear personal protective equipment like gloves, a mask, and long sleeves to avoid skin irritation and respiratory issues due to its fine glass particles. Rockwool, on the other hand, is denser and therefore, can be more cumbersome to maneuver. But its rigidity often allows for a friction fit between studs, which can simplify installation because it stays in place without the need for extensive fastening or support.

Suitability for Different Climates

Both rockwool and fiberglass provide thermal resistance; however, their performance can vary with climate. Rockwool is incombustible and can withstand high temperatures, making it preferable in areas where fire resistance is a significant concern. It’s also hydrophobic, meaning it repels water, which helps prevent mold and mildew growth in humid climates. Fiberglass insulation is suited for dry climates since it can lose insulating effectiveness when exposed to water. It’s also worth mentioning that if improperly installed in areas where it’s exposed to the elements, fiberglass can sag over time, diminishing its insulating properties.

Cost and Affordability

When you’re comparing Rockwool and fiberglass insulation, it’s crucial to consider both the upfront and long-term financial impacts of each material.

Initial Costs

Rockwool insulation is typically more expensive to purchase than fiberglass. You’ll find that the cost per square foot can vary depending on the R-value and the thickness of the material. Rockwool can cost between 10% to 25% more than fiberglass options for similar R-value ratings. For instance, if you’re insulating an average 1,500-square-foot attic to an R-38 value, the material cost for fiberglass might range from $0.12 to $1.20 per square foot, while Rockwool can range from $0.14 to $1.50 per square foot.

Long-Term Savings

The initial cost doesn’t tell the whole story, as energy savings over time can offset higher upfront costs. Rockwool boasts higher efficiency per inch compared to fiberglass, which means it can maintain its insulation capabilities better over time. You may find that your energy costs are reduced due to Rockwool’s ability to maintain a consistent temperature in your home more effectively. The long-term savings should consider energy efficiency and durability; Rockwool is less prone to sagging and settling and often lasts longer than fiberglass, potentially reducing replacement costs in the future.

Environmental Impact

When considering insulation options for your home, understanding the environmental impact is crucial. Both rockwool and fiberglass have distinct profiles in terms of sustainability and recyclability, which can influence your decision-making process.


Rockwool insulation is made from natural basalt rock and recycled slag, a byproduct of steel production. This gives rockwool a high sustainability score, as it leverages abundant resources and industrial byproducts that would otherwise go to waste. Moreover, rockwool’s production process is designed to conserve energy and reduce environmental impact, with some manufacturers even harnessing renewable energy sources.

In contrast, fiberglass insulation is produced from a mixture of sand and recycled glass. While sand is plentiful, it requires significant energy to melt down and form into fibers. The sustainability of fiberglass can vary depending on the manufacturer’s use of recycled glass and the efficiency of their furnaces. Companies with strong environmental policies may use up to 80% recycled content and invest in cleaner, more energy-efficient technology.


Rockwool insulation boasts excellent recyclability. After its service life in your home, it can be recycled again into new insulation products, contributing to a closed-loop system. However, the recycling infrastructure for rockwool is not as widespread, and you may need to research special facilities that can process this material.

Fiberglass insulation also offers recyclability options. Although not as straightforward to recycle as rockwool due to its fibrous nature, fiberglass can be melted down and reformed into new insulation. The challenge lies in the collection and transportation to specialized recycling centers, which are less common than those for traditional materials like paper or plastic.

Also Read: How to Choose the Right HVAC Filter for Your Home or Business



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