Toxic Chemicals in Insulation:

When choosing an insulation system, self-builders and architects are often faced with claims about "toxic" versus "natural" insulation. The reality is that virtually every insulation product contains chemicals in some form. The more important question is:

What is the health risk once the insulation is installed inside the building?

With a little help from our friend AI, we've compared the most common insulation materials based on their likely impact on occupants after installation, rather than during manufacture.

Common Insulation Materials

Insulation Type	Primary Constituents
Sheep Wool	Wool fibres, borate treatments
Cellulose	Recycled paper fibres, borates
Hemp	Hemp fibres, binders and additives
Cork	Expanded cork granules
Wood Fibre	Wood fibres, waxes and binders
Rockwool	Basalt rock, slag and resin binders
Glass Wool	Glass fibres and resin binders
EPS	Expanded polystyrene
XPS	Extruded polystyrene
PIR	Polyisocyanurate foam
PUR	Polyurethane foam
Phenolic Foam	Phenol-formaldehyde polymer

Occupant Health Risk Comparison

1 = Lowest Risk10 = Highest Risk

Insulation Material	Occupant Health Risk
Sheep Wool	1
Cellulose	1
Hemp	1
Cork	1
Wood Fibre	2
Rockwool	2
EPS	2
XPS	2
PIR	2
PUR	2
Glass Wool*	3
Phenolic Foam	3

*Primarily due to the potential for fibres to become airborne if disturbed during future refurbishment works.

Hazard vs Exposure

A common mistake is to judge insulation materials solely on the chemicals used during manufacture. Many construction products are produced using substances that require careful industrial handling but are transformed into stable materials once the manufacturing process is complete.

For example, polyurethane (PUR) insulation is formed through a chemical reaction that creates a stable polymer foam. Once cured, the material becomes inert and remains largely unchanged throughout its service life within the building envelope.

The same principle applies across many construction materials. Timber products, natural-fibre insulations and mineral insulations can all generate dust and airborne particles during manufacture, cutting and installation, yet present very low health risks once installed.

For building occupants, exposure is what matters. Most insulation products spend decades enclosed within walls, roofs and floors, with little or no direct contact with occupants.

When viewed in this way, the difference in occupant health risk between most mainstream insulation types is surprisingly small.

Why Sheep Wool Comes Out on Top

Sheep wool achieves the lowest occupant-health score due to its natural composition and minimal processing.

However, specification is always about balancing multiple factors, including:

• Thermal performance

• Wall thickness

• Structural requirements

• Embodied carbon

• Cost

• Buildability

For example, achieving the same U-values as high-performance foam insulation often requires considerably greater thicknesses of natural-fibre insulation, leading to deeper wall structures and increased material use.

Looking at all the factors...

The results show that once installed, most mainstream insulation products present a low health risk to occupants. Natural materials such as sheep wool, hemp and cellulose perform particularly well, but the gap between natural, mineral and synthetic insulation is far smaller than many marketing claims suggest.

For self-builders and architects, the focus should be on the performance of the complete building system rather than assumptions about the chemicals used to manufacture a product.

In a completed building, thermal performance, wall build-up, durability, moisture management and cost are often more significant differentiators than occupant health risk. The evidence suggests that once correctly installed, most modern insulation materials are stable, safe and suitable for use in healthy buildings.