New fire rating push puts Rockwool AFB insulation in the spotlight

Commercial builders are looking again at Rockwool AFB, a flexible stone wool batt for interior steel and wood stud walls that targets fire, acoustic and thermal performance in one package. A recent code-driven focus on noncombustible insulation is lifting its relevance in US projects.

Edited by ad hoc news New Releases & Launches Desk. Reviewed before publication on 06/16/2026 at 7:36 AM ET. Details in the imprint.

Heightened attention on fire safety in multifamily and commercial construction is pushing specifiers toward noncombustible insulation, and Rockwool’s AFB batt is one of the products benefiting from that shift. AFB is a flexible stone wool insulation batt designed for interior steel and wood stud assemblies where fire resistance, sound control and thermal performance must be balanced in a single material. In the US and Canada it is positioned primarily for partition walls, fire-rated floor-ceiling systems and corridor assemblies in offices, hotels, healthcare and education buildings.

What Rockwool AFB is designed to do inside the wall

AFB is manufactured from molten basalt rock and recycled slag spun into stone wool fibers, producing a dense, noncombustible insulation that inherently resists fire without added chemical flame retardants. According to the manufacturer, the product carries a melting point above 2,150°F (1,177°C) and achieves a flame spread index and smoke developed index of 0 in ASTM E84 testing, which allows it to contribute to fire-rated wall and floor-ceiling assemblies when installed per tested designs. The official Rockwool AFB product page details typical thicknesses from 1 inch to 6 inches and nominal densities of roughly 2.5 to 4 pounds per cubic foot, depending on configuration.

Beyond fire performance, AFB is marketed as an acoustic workhorse for interior partitions, particularly in multifamily and hospitality projects where sound transmission between units is a recurring complaint. The stone wool fiber structure and density help the batt reach sound transmission class (STC) ratings above 50 in common 2x4 and 2x6 stud wall build-ups when combined with appropriate drywall layers and resilient channels, according to test data referenced in Rockwool’s wall assembly guides. Those same guides note that stone wool’s dimensional stability helps keep cavities completely filled over time, supporting consistent acoustic performance compared with lighter, more compressible fibrous insulation types.

On the thermal side, AFB carries a published R-value of roughly R-4.2 per inch at 75°F mean temperature for the North American versions, placing it in a similar range to high-density fiberglass batts but with the additional benefits of noncombustibility and water repellency. Because it is designed for interior partitions, energy savings is usually a secondary benefit, but the material can still help moderate temperature differences between conditioned spaces and unconditioned shafts or corridors. The batts are friction-fit into standard stud spacings, allowing installers to cut pieces slightly oversize so they stay in place without mechanical fasteners in most vertical applications.

Contractors and building owners also weigh durability and moisture behavior when choosing between mineral wool and alternative insulations. Stone wool is hydrophobic and does not absorb bulk water; any moisture that contacts the batt tends to drain or evaporate while the fibers themselves remain structurally stable. Industry guidance from North American building science groups has highlighted mineral wool’s resistance to sagging, its non-nutritive nature with respect to mold and fungi, and its ability to maintain thickness and R-value after cyclic wetting and drying in laboratory tests. These characteristics have helped AFB find favor in high-occupancy buildings where long-term maintenance access to wall cavities is limited.

The product is available in multiple sizes tailored to North American framing, including 16 inch and 24 inch on-center widths and lengths around 48 inches that fit standard stud bays. Distribution runs through commercial building material suppliers and specialty insulation distributors rather than big-box retail, reflecting the product’s focus on professional installers and specification-driven projects. Rockwool has positioned AFB as part of a broader stone wool interior solutions lineup alongside products such as Rockwool Safe’n’Sound, with AFB more tightly linked to tested fire-rated wall and floor assemblies documented in its technical catalogues. A recent continuing-education article for architects from industry media has pointed to stone wool batts like AFB as a straightforward way to meet noncombustible insulation requirements under modern fire codes in Type I and II construction. A Construction Specifier feature on stone wool notes the growing role of mineral wool in both fire and acoustic design.

Rockwool Group, headquartered in Hedehusene, Denmark, reports that its stone wool insulation segment, which includes AFB and related interior products, is the company’s largest revenue contributor worldwide and a core focus of its North American growth strategy. In its latest annual report, management highlighted double-digit organic growth in North America driven by commercial and residential renovation demand and by stricter fire and energy codes in several US states and Canadian provinces. The company’s 2024 annual report emphasized continued investment in US and Canadian production capacity for stone wool batts and boards to shorten delivery times and reduce logistics costs for regional customers. Shares of Rockwool A/S (ISIN DK0010219153) are listed on Nasdaq Copenhagen, where the stock most recently traded in Danish kroner.

Rockwool AFB insulation in brief

• Product: Rockwool AFB
• Manufacturer: ROCKWOOL A/S
• Category: New Release/Launch - stone wool batt insulation for interior walls
• Launch date: Initially introduced in North America in the 2000s; current specification updated in recent years
• MSRP / Price: Sold through distributors; pricing varies by thickness and region, typically quoted per square foot or per bundle
• Availability: Commercial building material suppliers and insulation distributors across the US and Canada
• Target audience: Architects, engineers, contractors and building owners specifying or installing fire-rated and acoustically rated interior partitions
• Key differentiator / USP: Noncombustible stone wool batt combining fire resistance, acoustic performance, thermal insulation and dimensional stability for interior wall assemblies

This article was a.i.-assisted and editorially reviewed. Product information without warranty; prices and availability may change at short notice. Not investment advice and not a buy or sell recommendation. Trading involves risk up to and including the total loss of invested capital.