Isotherm vs Fabufill product comparison guide

Isotherm vs Fabufill: Compare and Decide

When it comes to insulating your ceiling or roof, polyester insulation is an option in South Africa thanks to its soft, non-itch feel, durability, and reliable thermal performance.

The two leading brands homeowners and contractors often compare are Fabufill and Isotherm. Both are made from 100% recycled polyester and help maintain a comfortable indoor temperature, but there are key differences that could influence which one is best for your project.

On this page, we’ll break down Isotherm vs Fabufill on SABS approval, density, certified R-values, fire safety, and long-term peace of mind — so you can make an informed decision for your home.

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Isotherm vs Fabufill — Quick Overview

Fabufill and Isotherm are both locally manufactured polyester insulation products. Made from recycled PET plastic bottles, they’re safe to handle, completely non-itch, and designed for residential ceiling applications across South Africa. They help reduce electricity costs by slowing heat flow through your ceiling, keeping your home cooler in summer and warmer in winter.

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While they look similar on the surface, the big difference is that only Fabufill carries active SABS approval, meaning its performance has been independently tested and verified. This is a crucial distinction for anyone wanting guaranteed results and compliance with South African building standards.

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Isotherm vs Fabufill — Quick Comparison Table

Feature	Fabufill	Isotherm
Type	100% recycled polyester	100% recycled polyester
SABS approved?	✅ Yes (certified at 10kg/m³)	❌ No (lost SABS mark)
Density	±10kg/m³ (officially tested)	±11.5kg/m³ (claimed only)
R-Value @145mm	±3.35 (certified)	±3.37 (manufacturer claim)
Fire rating	B-class	B-class
Handling & comfort	Soft, non-itch, easy to install	Soft, non-itch, easy to install

SABS Approval & Certification

This is where Fabufill clearly stands out. It’s fully SABS approved, which means its density, R-values, and fire safety have been independently tested and certified. You’re not just taking the manufacturer’s word for it — the product you buy is proven to perform exactly as stated.

By contrast, Isotherm no longer holds its SABS mark. While it was once certified, that approval has lapsed, so all technical specs, including its R-value and density, are now based purely on manufacturer claims.

For many homeowners, builders and architects, this lack of third-party verification is a serious factor when choosing insulation that’s expected to perform reliably for decades.

Density & R-Values

When it comes to density — a critical metric for insulation effectiveness — here’s how these two products compare:

Fabufill is certified at ±10kg/m³, officially verified through rigorous SABS testing. This guarantees that the insulation you install meets the precise performance promised on the label.
Isotherm is marketed at a slightly higher ±11.5kg/m³, but this figure is not backed by current independent certification, making it a manufacturer-stated claim.

As for thermal resistance, both products appear very similar on paper:

Fabufill offers a certified R-value of ±3.35 at 145mm thickness, proven through SABS approval.
Isotherm advertises a slightly higher claimed R-value of ±3.37 at 145mm, but without active SABS testing to validate this figure.

So while Isotherm’s R-value is marginally higher on spec sheets, only Fabufill’s performance is officially verified, giving you documented assurance that your insulation will actually achieve its stated energy savings.

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Thermal & Acoustic Performance

Both Fabufill and Isotherm excel at their primary purpose: thermal insulation, helping stabilize indoor temperatures, reduce heating and cooling costs, and improve year-round comfort.

When it comes to sound, polyester insulation like Fabufill and Isotherm does provide some reduction in airborne noise, offering a quieter environment than an uninsulated ceiling. However, it’s important to understand that polyester is not engineered for high-level acoustic insulation the way glasswool products like 135mm Knauf or 135mm Aerolite are.

If noise control is your top concern, a higher-density glasswool might be more suitable. But for most homeowners focused on energy efficiency and a comfortable, non-itch product, polyester is an outstanding choice.

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Installation & Handling

Both Fabufill and Isotherm share excellent handling qualities:

Soft, lightweight, and completely non-itch, making them far easier to work with than traditional glasswool.
Easy to cut and fit snugly between roof trusses, above the ceiling board.
Safe for installers and homeowners, with no added chemicals, binders, or formaldehyde.

Whether you’re doing a professional installation or a DIY project, both are straightforward to work with, though many homeowners still prefer professional fitting for guaranteed coverage and neatness.

Pricing & Value

In terms of pricing, Fabufill and Isotherm are generally in the same ballpark, with small differences depending on your supplier, region, and the thickness selected. However, because Fabufill’s density and R-values are independently verified by the SABS, you’re getting more than just a product — you’re buying guaranteed, tested performance.

This often makes Fabufill the smarter long-term value, ensuring your insulation truly delivers on promised savings and compliance.

So Which Should You Choose?

While both Fabufill and Isotherm are safe, effective polyester insulation options that will make your home more energy efficient, Fabufill stands out as the clear choice for peace of mind and proven compliance.

Choose Fabufill if you want full confidence that your insulation meets South African standards, with SABS-certified density and R-values independently tested to deliver exactly what’s promised. It’s the smart option for homeowners, builders and architects who prioritize guaranteed thermal performance and regulatory compliance — ensuring your investment pays off for decades.

Isotherm remains a viable alternative, but without active SABS certification, its figures are purely manufacturer-declared, leaving a gap in third-party assurance that’s worth carefully considering.

Get a Quote on Fabufill or Isotherm Insulation

We supply and install both Fabufill and Isotherm polyester insulation, delivering quality installations across Johannesburg, Pretoria, Centurion, Durban, and Cape Town.

Or contact us today for a free quote — we’ll help you compare options and choose the best insulation for your needs.