ROOF INSULATIONS · PRODUCT COMPARISON
Knauf vs Isotherm insulation.
Choose with confidence.
Two different materials. One practical decision. Compare thermal resistance, fire classification and roll coverage before choosing insulation for your home.
Comparing 135mm Knauf Ceiling Roll with the specified 145mm Isotherm polyester product.
GLASS MINERAL WOOL
135mm Knauf
R3.38Published SA product R-value9 m² per 1.2m-wide roll
RECYCLED PET POLYESTER
145mm Isotherm
R3.37Published product R-value at 11.5 kg/m³6 m² per 1.2m-wide roll
Range images shown. Match your order to the specified thickness and grade. Product data: sources 1–2.
THE PRACTICAL VERDICT
Similar published R-values.
Different reasons to choose.
A useful Knauf vs Isotherm insulation comparison starts with the exact products. These two options have closely matched published product R-values. A brand name alone cannot tell you which quotation meets your needs.
Our recommendation: start with Knauf when a non-combustible insulation material is your priority. Consider Isotherm when you specifically prefer polyester. Check the supplied grade, installation requirements and delivered price before ordering.
Your decision should rest on documented specifications and a complete quote—not star ratings or promises of identical savings in every home.
THE DETAILS, SIDE BY SIDE
Knauf vs Isotherm insulation comparison
The figures below refer to the selected ceiling products, not every product sold under either brand.
| What you are comparing | 135mm KnaufCeiling Roll / Loft Roll | 145mm Isotherm11.5 kg/m³ published specification |
|---|---|---|
| Insulation material | Glass mineral wool with ECOSE® binder | Thermally bonded polyester from recycled PET |
| Nominal thickness | 135mm | 145mm |
| Published product R-value | 3.38 m²·K/W South African declared value | 3.37 m²·K/W Specified 11.5 kg/m³ product |
| Roll dimensions used here | 7.5m × 1.2m | 5m × 1.2m |
| Coverage per roll | 9 m² | 6 m² |
| SANS 428 fire register entry | A/A1/1 Knauf also declares Euroclass A1 | B/B1/2 H Horizontal-use entry in the register |
| Working with the material | Flexible mineral wool; follow the product handling instructions. | Soft polyester; check cutting method and fit before starting. |
| Best way to compare price | Quoted roll price ÷ 9 m² | Quoted roll price ÷ 6 m² |
| Before you order | Confirm thickness, roll format and pack coverage. | Confirm thickness, density, product R-value and pack coverage. |
Swipe the table sideways to see both products.
Showing all 9 comparison points.
BEYOND THE BRAND NAME
What the differences mean for your home
Read Knauf vs Isotherm insulation specifications in context. A good buying decision considers the whole job, from the first measurement to the final fitted roll.
Compare the correct thickness and grade
In this Knauf vs Isotherm insulation comparison, the main thermal figures are close. That does not make every thinner or lower-density roll equivalent. The Isotherm literature, for example, lists different grades at the same 100mm thickness.
Ask the supplier to put the product specification on the quote. A photograph, brand name or thickness alone leaves too much room for misunderstanding.
Keep the classifications separate
Fire performance is a meaningful difference in Knauf vs Isotherm insulation. The recorded SANS classifications differ, and Knauf’s current Ceiling Roll datasheet identifies the product as non-combustible Euroclass A1.
A material classification is not a fire-resistance rating for your entire ceiling. Keep lighting, flues and other heat sources within their specified installation requirements, whichever material you choose.
Choose a material you can fit properly
Handling is another part of Knauf vs Isotherm insulation. Polyester has a textile-like feel; Knauf uses its ECOSE® binder to improve mineral wool handling. Both still need careful measuring and fitting.
Plan around the access hatch, obstructions and ceiling framing. Keep ventilation routes clear, follow the relevant handling guidance and avoid compressing the insulation to force it into a space.
Ask what is being measured
A Knauf vs Isotherm insulation sound comparison needs matching acoustic test conditions. A product absorption figure is not a promise of the same noise reduction through every roof. Avoid choosing from unsupported percentage claims.
Likewise, do not treat a blanket as a roof-leak repair. Investigate leaks or persistent condensation before installation and check the roof’s ventilation and moisture-control needs.
TURN THE COMPARISON INTO A SHOPPING LIST
Knauf vs Isotherm insulation cost calculator
A roll price can be misleading when coverage differs. Enter your ceiling area and the quoted prices for these exact products to compare whole-roll material costs.
Prices are optional. Use current VAT-inclusive prices for 135mm Knauf and the specified 145mm Isotherm. The allowance is adjustable, not a site recommendation.
135mm Knauf
145mm Isotherm
100 m² + 5% allowance = 105 m² to cover. Add both roll prices to compare material totals.
Estimate only. Excludes installation, delivery and accessories. Quantities use 9 m² and 6 m² rolls respectively and round up to whole rolls. Confirm measurements and coverage before ordering.
For a fair Knauf vs Isotherm insulation price comparison, include delivery and installation in the final quotation too. A lower cost per roll does not necessarily mean a lower cost for the completed ceiling.
BEFORE YOU BUY
Three checks that prevent an expensive mismatch
Confirm the supplied product
Finish your Knauf vs Isotherm insulation comparison with the exact thickness, grade and coverage written on the quotation. Ask for the supporting datasheet if the description is incomplete.
Confirm the work involved
Ask whether the price covers materials only, delivery or installation. Note access restrictions, existing insulation and any preparation needed. Separate these costs so you can compare quotations fairly.
Check the complete roof design
A product comparison cannot establish compliance for an individual building. Have the required roof performance and installation details checked for your actual project.
STRAIGHT ANSWERS
Knauf vs Isotherm insulation FAQs
Use these answers to narrow your choice, then confirm the details of the product you will actually receive.
Which is better: Knauf or Isotherm?
In Knauf vs Isotherm insulation, there is no single answer for every project. Knauf is the clearer choice where non-combustible material is required. Isotherm is an option for buyers who specifically want polyester. Compare the specified products and the complete quotation.
Does thicker insulation always perform better?
Thickness alone is insufficient when comparing different materials or grades. Check the declared R-value for the exact product and how it is intended to be installed. Do not assume that a thicker roll automatically outperforms a thinner product from another range.
Are product R-value and total R-value the same?
No. Product R-value describes the insulation itself; total R-value relates to the roof-and-ceiling assembly. A Knauf vs Isotherm insulation comparison must keep those two figures separate. Do not compare one product’s blanket value with another quotation’s complete roof value.
Which product costs less for my ceiling?
Use current quotations and the calculator above. Knauf vs Isotherm insulation cost depends on the roll price, coverage, whole-roll rounding, delivery and any installation work. Check that both quotations use the same VAT basis and include the same work.
Can I fit either product myself?
That depends on safe access and your ability to follow the product instructions. A soft material does not remove roof-space hazards. Avoid walking on ceiling boards, keep ventilation paths open and arrange professional help where access or electrical work requires it.
Will either product fix roof leaks or eliminate noise?
No insulation purchase should be based on those promises. Fix moisture problems first. For sound control, assess the entire roof or ceiling construction and obtain suitable acoustic advice when noise reduction is a main project requirement.
READY FOR THE NEXT STEP?
Get the right specification.
Then get a proper quote.
Still weighing up Knauf vs Isotherm insulation? Send us your ceiling area, suburb and preferred product. We can help you check the supply options and prepare your enquiry.
Specification sources & comparison notes
- Knauf Ceiling Roll / Loft Roll datasheet, September 2025 (PDF).
- Brits Nonwoven Isotherm manufacturer brochure, hosted by Pelican (PDF). Thermal figures here use the stated 11.5 kg/m³ grade.
- TIPSASA fire classification register, June 2024, Table 1 (PDF).
- Knauf Insulation: ECOSE® Technology.
Sources reviewed October 2026. Published values and product ranges can change; request current documentation for the stock quoted. Older brochure climate-zone tables are not used here to determine present-day regulatory compliance.
