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Cellulose Insulation

Recycled paper insulation: how it is installed, how it performs, and what to check

2 min readUpdated November 2026

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What is cellulose insulation?

Cellulose insulation is made mostly from recycled paper, shredded into fibres and treated with additives for fire and pest resistance. It is usually blown, injected, or damp-sprayed into place by trained installers, which helps it fill irregular spaces around joists, pipes, and cables.

How does it perform?

Declared thermal conductivity is typically about 0.038-0.040 W/mK and varies by product and installation method. One UK product, for example, declares 0.038 W/mK when dry installed and 0.039 W/mK when sprayed with moisture.

TopicDetail
ThermalCompare the declared value for the installation method you will use.
DensityFollow the required density for the application. It affects performance and settling.
MoistureHygroscopic and vapour open, so it can work in breathable build-ups if the design allows it.

Installation methods

Installation quality has a big effect on performance, so ask how the installer checks the result.

  • Open blown

    Typical use
    Horizontal lofts
    What to check
    Settled depth, eaves ventilation, and access boards

  • Dense pack

    Typical use
    Closed timber frame walls, sloped roofs, and floors
    What to check
    Density, membrane strength, and voids

  • Damp spray

    Typical use
    Open wall cavities
    What to check
    Moisture content, drying time, and adhesion

Tip. Ask for density records from the job. Weighing the bags used and comparing them with the filled volume is a simple check that a cavity holds the required amount.

Fire class and additives

Fire class depends on the product and how it is installed. Published examples range from B-s2, d0 to E, so check the current documents for the exact product rather than assuming all cellulose is the same. It is also important to keep insulation clear of flues, recessed lights, and other hot services, following the manufacturer's instructions.

Formulations differ. If you want to avoid a specific substance, ask for a safety data sheet and full ingredient information.

Where it works best

Cellulose is good at filling awkward spaces, as long as the space is suitable and can be properly contained.

  • Lofts

    Good
    Check
    Ventilation, roof leaks, and settled depth

  • Timber frame walls and cassettes

    Good
    Check
    Dense pack density, fire, and airtight layer

  • Sloped roofs

    Good
    Check
    Membranes, ventilation, and moisture design

  • Suspended timber floors

    Possible
    Check
    Containment and subfloor ventilation

  • Masonry cavity walls

    Check
    Check
    Product approval, wall condition, and exposure

  • Damp or leaking structures

    Unsuitable until fixed
    Check
    Repair first and allow drying

Trade-offs

You usually need a trained installer and specialist equipment. Dust needs controlling during installation. Cellulose must be kept dry and well contained, as loose material can settle if the density is wrong and is messy to remove from a closed cavity.

Check for a product-specific EPD rather than assuming its carbon figure, as additives and transport still count.

Using Matera

Ask suppliers for recycled content, declared conductivity, required density, fire class, and additives, plus whether they can recommend trained installers near your project. Compare installed prices, as the cost of labour matters more here than with roll insulation.

Sources

Where the facts in this guide come from. Standards and guidance change, and some sources are suppliers or trade sites, so check the original before relying on a detail.

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