ECO FRIENDLY HOMES · MATERIALS EXPLAINED
Isotherm insulation.
Know what goes above your ceiling.
Understand Isotherm insulation benefits, thicknesses and R-values. Compare the right grade, plan your quantity and make an informed choice for your home.
Explore the specifications
What is Isotherm insulation?
Isotherm insulation is a flexible polyester blanket used to improve thermal insulation above ceilings. Manufacturer literature describes thermally bonded fibres made from recycled PET.
The blanket is a concealed layer rather than a decorative ceiling finish. It belongs in a suitable ceiling or roof assembly, with the supporting ceiling, services and access considered together. It does not replace the ceiling board or a waterproof roof covering.
Choosing Isotherm insulation starts with the problem you want to solve. An uncomfortable upstairs bedroom, a cold living room and a noisy metal roof may need different combinations of work. Describe the room, roof arrangement and existing insulation before choosing a pack.
For the broader material choices, see our types of ceiling insulation guide. This page concentrates on understanding and specifying the polyester product.
Isotherm insulation benefits and limitations
Thermal comfort
A suitable blanket resists heat transfer through the ceiling. That can help rooms retain warmth in winter and limit unwanted heat gain from a hot roof space.
A polyester option
The material offers an alternative for buyers who specifically prefer polyester to glasswool. Personal preference should sit alongside the required technical performance.
Potential for an upgrade
An accessible roof space may allow insulation work while keeping the visible ceiling. A site assessment establishes whether that approach suits the property.
Recycled feedstock
Recycled PET gives the material a waste-reuse story. Responsible selection also considers performance, durability, transport and what happens at the end of use.
These Isotherm insulation benefits need realistic expectations. There is no universal temperature improvement or electricity saving for every house. Heating and cooling habits, glazing, draughts, shading and the insulation already present all influence the result.
For noise, request evidence for the proposed construction. An absorbent cavity layer and a sound-isolating ceiling assembly serve different purposes. A thermal blanket alone is not a promise that rain, traffic or neighbouring-room noise will disappear.
Isotherm insulation thicknesses and R-values
Use the table as a reference for asking the right questions. These are figures from an older manufacturer brochure, not a guarantee that every currently supplied pack has the same specification. Obtain the current datasheet for the actual product quoted.
| Thickness | Density | Material R-value | Nominal length |
|---|---|---|---|
| 145mm | 11.5kg/m³ | 3.37 | 5m |
| 135mm | 11.5kg/m³ | 3.14 | 5m |
| 100mm | 11.5kg/m³ | 2.33 | 6m |
| 100mm | 8.5kg/m³ | 1.57 | 6m |
| 75mm | 8.5kg/m³ | 1.18 | 8m |
| 50mm | 8.5kg/m³ | 0.79 | 10m |
Source: Brits Nonwoven’s Isotherm brochure, hosted by Pelican Systems. The brochure lists 750mm and 1,200mm widths. Its historical climate-zone recommendations are not reproduced as current compliance advice.
A higher R-value means greater resistance to heat flow when figures are compared on an equivalent basis. Material R-value describes the insulation layer. Total roof-system performance also involves the other layers, air spaces and construction details.
Do not turn an Isotherm insulation R-value into an automatic compliance statement. Ask the project designer or competent installer to identify the applicable requirement and supporting calculation for your actual roof. A generic allowance for roof and ceiling materials cannot describe every building.
Why 100mm Isotherm insulation needs a grade check
Two quotations can both say “100mm” while describing different products. The reference table shows why a thickness-only comparison can mislead. Check the grade and declared performance before deciding which quote offers better value.
On an Isotherm insulation order, request an identifiable product description rather than “green ceiling insulation”. Include the thickness, density or grade identifier, material R-value, roll dimensions and number of rolls per pack.
Ask for any proposed substitution in writing. If the specified grade is unavailable, the replacement should be assessed against the project requirements before delivery. A similar colour, a familiar brand name or an apparently equivalent thickness is not enough information.
Keep the quotation, datasheet and a photograph of the delivered label with your project records. This creates a useful reference if you extend the insulation later, query a delivery or compare an additional layer.
How much Isotherm insulation will you need?
Measure the ceiling area to be insulated. Do not substitute the sloping roof surface area, a rough estate-agent floor area or the number of bedrooms. Separate spaces that require insulation from garages, verandas and other areas outside the agreed scope.
Worked example: a 72m² ceiling
If the selected roll is 5m × 1.2m, its nominal area is 6m². A 72m² ceiling therefore needs 72 ÷ 6 = 12 rolls before a project-specific cutting allowance.
If the same length is only 0.75m wide, coverage is 3.75m². The calculation becomes 72 ÷ 3.75 = 19.2, rounded up to 20 rolls before the allowance. Confirm how many rolls the supplier includes in a pack.
This example shows why Isotherm insulation quantities depend on width as well as thickness. Ask the installer to consider the layout, irregular edges, access hatch and usable offcuts. The right cutting allowance comes from that layout; it is not automatically the same percentage for every home.
For an existing house, request the measured area on the quotation. If some rooms cannot be reached, have those exclusions identified before accepting an installation price. A low total can conceal a smaller scope of work.
Comparing Isotherm insulation with Aerolite and Knauf
Compare products against the same brief: required thermal performance, available depth, relevant fire requirements, installed area and total project cost. A material preference can then help you choose between technically suitable options.
| Compare | Request | Why it matters |
|---|---|---|
| Thermal performance | Declared material R-value and test basis | Equal thickness does not necessarily mean equal performance. |
| Fire evidence | Relevant classification and scope | A product result must suit the proposed application. |
| Quantity | Actual coverage and pack contents | Pack prices cannot be compared without coverage. |
| Installation | Measured area and included work | Access, preparation and exclusions affect value. |
| Final cost | VAT, delivery, labour and extras | The delivered, installed total is the useful budget. |
Our Aerolite Soft Touch guide and Knauf ECOSE guide cover those alternatives in detail. Keep the shortlisted specifications together rather than selecting a universal winner from brand names alone.
Isotherm insulation fire classification and certification
Fire classification and product certification answer different questions. Neither should be reduced to an unsupported claim that a whole house is “fireproof” or that every possible installation is approved.
The December 2024 TIPSASA register records 145mm Isotherm, manufactured by Brits Nonwoven, as B-s1, d1 under SANS 53501-1, with report IT 24-09-00060 dated 17 September 2024. This is a dated reference, not a claim that it is the latest register.
That reaction-to-fire result is not an A1 classification or a fire-resistance duration for a completed ceiling. Obtain the current report and confirm which supplied grades, thicknesses, densities and applications its scope covers. Avoid applying one listed result to an unidentified pack.
At our check on 2 November 2026, Agrément South Africa’s active-certificate list included 2005/320: Isotherm Thermal Insulation. The published certificate has defined product and installation conditions. Request the current certificate documentation and confirmation that the quoted product and proposed use fall within it.
For an Isotherm insulation specification, ask for the actual evidence required by the project. An Agrément listing, an SABS mark and an individual test report are not interchangeable labels.
Planning an Isotherm insulation installation
A useful Isotherm insulation installation starts with a site assessment. Tell the installer whether the ceiling is new or existing, where the access hatch is and whether you have noticed leaks, staining or damaged boards.
- Resolve the roof condition. Investigate leaks and moisture problems before covering the area. Insulation is not a waterproofing repair.
- Check the services. Identify downlights, transformers, flues, wiring and equipment. Use the clearances and protection required for the actual fittings and insulation system.
- Plan safe access. Ceiling boards are not a walking surface. Agree how the installer will reach difficult areas without damaging the ceiling or roof structure.
- Preserve the intended performance. The blanket should fit the planned arrangement without unnecessary gaps or compression. Keep required roof ventilation paths open.
- Record the finished work. Request photographs, product identification, treated area and any remaining inaccessible sections.
Do not assume a soft, glass-fibre-free blanket makes a dusty roof space risk-free. Handling precautions should reflect the current product instructions and the site conditions. Questions about an individual’s sensitivities should not be answered with a blanket “allergy-proof” marketing promise.
Adding to existing insulation
Before adding Isotherm insulation, have the existing layer assessed for condition, continuity and suitability. Adding material over a roof leak or badly disturbed insulation does not resolve the original problem.
Ask whether a top-up can be installed continuously without compromising services, ventilation or access. The combined assembly needs assessment; adding the thicknesses on two invoices does not establish a verified roof-system performance.
Is Isotherm insulation an environmentally responsible choice?
Recycled feedstock is one consideration, but an environmental decision needs more than the word “green”. Ask what evidence supports the current product’s recycled-content claim and whether an environmental product declaration or other independently checked information is available.
Consider the useful life of the installation, material quantities, transport and the energy it may help you avoid. A well-planned installation with documented performance is a more useful purchasing objective than selecting a product solely from packaging colour.
Also ask how clean offcuts and removed material can be handled locally. Being technically recyclable does not mean a nearby recycler accepts used insulation. Confirm an actual collection or processing route before promising that material will be recycled.
Understanding Isotherm insulation prices
Isotherm insulation prices depend on the selected product and the order. Check live pricing or request a written quotation; an older blog price can omit delivery, VAT or a change in pack contents.
For materials, divide the pack price by its confirmed coverage to compare cost per square metre. Use that comparison only after checking that each option meets the intended specification. A lower cost per square metre is not automatically better value if the product cannot deliver the required result.
For installation, send the ceiling area, suburb, photographs of access, details of existing insulation and your preferred timing. Ask whether preparation, removal, disposal, protection around fittings and making good are included where relevant.
Isotherm insulation: common questions
Is Isotherm the same as Isoboard?
No. This guide concerns a flexible polyester blanket. Isoboard is a rigid XPS board product. The products have different forms and installation details. For a visible insulated ceiling option, read our Isoboard ceiling benefits guide.
Is 145mm always the correct thickness?
No single thickness is a universal answer. Confirm the grade, required thermal performance, available depth and proposed roof assembly. A named thickness on its own does not demonstrate that a project meets its requirements.
Can I put stored boxes on top of the blanket?
Plan storage separately so loads are supported appropriately and insulation is not crushed. Ask about a suitable access or storage arrangement before work starts. Loose boards placed over insulation are not automatically a safe storage platform.
Will the insulation stop roof leaks or condensation?
It is not a roof repair. Have the moisture source assessed and the required ventilation maintained. If insulation becomes wet or contaminated, arrange an inspection rather than assuming the product’s material description guarantees that it can remain in place.
Can I order from the product name alone?
For Isotherm insulation, request the exact grade, thickness, declared performance and pack dimensions. Confirm those details on the written quotation and delivered labels. This is especially useful when comparing several suppliers or accepting a proposed substitution.
Where can I arrange installation in Cape Town?
Contact Cape Ceilings & Drywalling with your location, approximate area and access details. Its Isotherm service is available on request, with product and project requirements confirmed before quoting.
TAKE THE NEXT STEP
Choose the product.
Plan the installation.
Use the specification questions above to turn an Isotherm insulation enquiry into a clear quotation for your home.
Business relationship: Eco Friendly Homes directs product and installation enquiries to our associated businesses, Roof Insulations and Cape Ceilings & Drywalling.
References and editorial notes
Product reference: manufacturer brochure. Certification: Agrément active list and published certificate. Fire evidence: TIPSASA December 2024 register. General principles: U.S. Department of Energy heat-flow guidance and Knauf’s explanation of sound absorption and isolation.
Sources checked 2 November 2026. Older documents are identified as references rather than current stock specifications. International building-science guidance is used for general principles, not South African compliance requirements.