Insulation Matters More Than You Think
A closer look at air quality, chemical exposure, and the materials we live inside
When we talk about healthy homes, insulation is rarely part of the conversation. We focus on finishes, paint colors, water filters, or air purifiers, while the largest material surface area in the building remains invisible and unquestioned.
Yet insulation quietly determines much of a home’s long-term impact on respiratory health, nervous system load, chemical exposure, and overall indoor air quality. It sits inside walls, ceilings, and floors for decades. Whatever it contains, releases, or sheds becomes part of the internal environment we breathe every day.
Below is a clear comparison of the most common insulation materials used in U.S. construction: fiberglass, mineral wool (including rock wool), and real sheep’s wool insulation, with particular attention to formaldehyde exposure, embodied energy, biodegradability, and human health.
Why insulation choice affects indoor air quality
Most insulation materials are not inert. They are manufactured using binders, adhesives, or treatments that can off-gas volatile organic compounds (VOCs), shed fibers into air pathways, or break down slowly over time.
Because insulation is often installed directly adjacent to living spaces, HVAC systems, and pressure differentials, even “sealed” materials can influence indoor air quality through micro-leakage, renovation disturbance, or aging assemblies.
For people with respiratory sensitivity, autoimmune conditions, children, or those intentionally building low-toxic environments, insulation is not a neutral choice.
Fiberglass insulation
What it is
Fiberglass is made by melting sand and recycled glass at high temperatures and spinning it into extremely fine glass fibers. These fibers are held together with synthetic chemical binders.
Air quality and handling safety
Fiberglass fibers are small, brittle, and easily airborne. During installation, removal, or disturbance, fibers can enter the lungs, eyes, and skin. Even after installation, fiberglass can shed microscopic particles into attics and wall cavities, especially if air sealing is imperfect.
Protective equipment is required during handling for a reason. Fiberglass is a known respiratory irritant, and its fine, sharp fibers are particularly problematic for sensitive individuals.
Chemical binders and formaldehyde
Historically, fiberglass insulation has been one of the most significant sources of formaldehyde exposure in residential construction. While many manufacturers now market “formaldehyde-free” versions, these still rely on synthetic binders and resins that can off-gas other VOCs, especially when new or exposed to heat.
Formaldehyde is a known respiratory irritant and carcinogen, linked to asthma exacerbation, headaches, and long-term health effects. Even low-level chronic exposure matters when it is constant.
Environmental impact
Fiberglass requires high-temperature industrial processing, resulting in significant energy expenditure. It is not biodegradable and is rarely recycled after removal. Once installed, it eventually becomes construction waste.
Summary
Fiberglass is inexpensive and widely available, but it carries the highest burden in terms of fiber irritation and long-term indoor air quality risk.
Mineral wool and rock wool insulation
What it is
Mineral wool is a category that includes rock wool (made from basalt stone) and slag wool (made from steel industry by-products). These materials are melted at extremely high temperatures and spun into dense fibers.
Rock wool is often marketed as a healthier alternative to fiberglass, but it is important to understand what that claim does and does not mean.
Air quality and handling safety
Mineral wool fibers are thicker and heavier than fiberglass, which makes them less airborne. However, they still cause skin, eye, and lung irritation during handling, and protective equipment is recommended.
Once installed and well sealed, mineral wool is generally more stable than fiberglass, but it remains a fibrous material that can shed when disturbed.
Chemical binders and formaldehyde
Most mineral wool products use phenol-formaldehyde or similar synthetic binders. Some brands now offer low-formaldehyde formulations, but they are still chemically bound products.
While off-gassing is typically lower than fiberglass, mineral wool does not actively improve air quality, nor does it neutralize chemical pollutants.
Environmental impact
Mineral wool has one of the highest embodied energy profiles of any insulation material due to the extreme heat required for production. It is non-renewable, non-biodegradable, and rarely recycled.
Summary
Mineral wool performs well for fire resistance and sound control and is generally preferable to fiberglass from a durability standpoint. From an ecological and physiological perspective, it remains an industrial compromise.
Real wool insulation (sheep’s wool)
What it is
Sheep’s wool insulation is made from renewable wool fibers that are mechanically processed into batts or rolls. It is typically treated with borate salts for pest resistance, a low-toxicity mineral compound with a long history of use.
Air quality and handling safety
Sheep’s wool is safe to handle with bare hands. It does not shed irritating fibers, does not require protective equipment, and does not become airborne in the same way mineral fibers do.
More importantly, wool actively improves indoor air quality. Wool fibers naturally bind and neutralize formaldehyde, nitrogen oxides, and other VOCs, permanently locking them into the fiber structure rather than re-releasing them into the air.
Chemical exposure and formaldehyde
Unlike synthetic insulation, wool does not require formaldehyde-based binders. Its structure is self-supporting and naturally elastic.
This makes wool one of the only insulation materials that does not merely reduce harm, but actively mitigates chemical exposure inside the home.
Environmental impact
Sheep’s wool is renewable, biodegradable, and compostable. It requires significantly less energy to process than mineral-based insulation and does not become persistent waste at the end of its life.
Moisture and durability
Wool regulates moisture rather than trapping it. It can absorb and release humidity without losing insulation performance, reducing mold risk and supporting healthier building assemblies.
Summary
From a human health and ecological standpoint, sheep’s wool is the most aligned insulation material available. Its higher upfront cost reflects material integrity, not added chemical complexity.
Formaldehyde exposure and the built environment
Formaldehyde is one of the most common indoor air pollutants in modern construction. It is used in resins, binders, glues, and finishes, and it accumulates silently in tightly sealed homes.
Insulation is often overlooked as a source, yet it can represent a large, continuous exposure surface. Choosing materials that reduce or eliminate formaldehyde load is not about perfection. It is about cumulative burden.
The body does not differentiate between sources. It only experiences total exposure.
The larger question: what do we want our homes to do?
A home can be a passive container, or it can be an active participant in health.
Industrial insulation materials are designed primarily for performance metrics and cost efficiency. Natural materials tend to support regulation, buffering, and resilience over time.
When we choose insulation, we are not just choosing R-value. We are choosing what our nervous systems, lungs, and immune systems interact with every day.
Final perspective
Fiberglass is the most chemically and physically irritating option and offers the least benefit to indoor air quality.
Mineral wool is more stable and durable than fiberglass but remains energy-intensive, chemically bound, and non-biodegradable.
Real wool insulation is renewable, non-toxic, biodegradable, and uniquely capable of improving indoor air quality rather than merely avoiding harm.
Healthy buildings are not built from trends. They are built from materials that respect biology, time, and the quiet intelligence of the body.
