Rockwool Fibertex and Fibermesh: Picking by Density and Temperature

The number in a Bradford Rockwool name is the service temperature, not the R-value. Fibertex runs at 350, 450, 650 and 820 °C, at nominal densities of 60, 80, 100 and 110 kg/m3. Fibermesh is the same stone wool stitched to a steel mesh, in two grades. Choose on plant temperature first, then on the shape being wrapped.

What the number actually means

Six grades carry the naming: Fibertex 350, 450, 650 and 820, then Fibermesh 450 and 650. The number is the temperature the material is rated to work at. Bradford's Fibertex 820 page reads "Unfaced boards, blankets and strips can withstand temperatures up to 820°C", and the same sentence runs on the other pages with the number swapped. Its 2020 HVAC and Industrial Insulation Product Selector lists the densities: 350 at 60 kg/m3, 450 at 80, 650 at 100, 820 at 110. Bradford writes stone wool in the 350 and 450 statements and Rockwool in the rest, meaning the same thing.

There is a catch before quoting a grade to a certifier. None of the five Product Technical Statements we serve states a maximum service temperature. The only temperature in them is fusion temperature to ASTM E 794, onset melting above 1200 °C, which is where the fibre melts rather than where the product stops working. Bradford's Supertel glasswool statement does print one in its Additional Product Data table, so the omission is specific to this range. Cite the product page or the selector, and expect to be asked where the figure came from.

On a boiler or a flue, glasswool is not an alternative. Bradford caps its HVAC glasswool well below the mildest Fibertex grade, as the HVAC duct insulation range sets out. Where stone wool earns its price against the other materials is in insulation materials compared.

The six grades side by side

Nobody publishes these next to each other, which is the reason for the table, and the last column repays a second look.

R-values come from the statement covering the code we sell: PTS065 E for the 350, PTS066 F for the 450, PTS067 G for the 650, PTS068 J for the 820, all declared to AS/NZS 4859.1 at 23 °C. Our 25 mm Fibermesh 450, code 114144, is in no Bradford document read here.

What the grade ladder does not buy

Density nearly doubles across the range and the temperature rating more than doubles. Thermal resistance at the same thickness barely moves.

Read across any row and the spread is R0.05 at 50 mm and R0.15 at 75 mm. The 820, top of the range at 110 kg/m3, ties the 350 for poorest at 50 mm and is outright poorest at 75 mm. Paying up a grade for a better insulator is money spent on the wrong thing. Thickness buys thermal resistance. The grade buys the right to be there at all.

Plain blankets track the boards: R0.74 at 25 mm in the 450, 650 and 820, R1.45 at 50 mm in the 450 and 650. The 13 mm strip is R0.39. Density is doing other work here, and where that work is sound absorption the argument is in acoustic versus thermal insulation.

Fibertex or Fibermesh, and which wire

Fibermesh is stone wool with a wire mesh stitched to one face, on a roll: 5 m at 50 mm, 3 m at 75 mm, both 600 mm wide. Bradford's statement and web table carry four codes per grade, galvanised and stainless at each thickness. Our Fibermesh 450 adds a fifth, a 25 mm galvanised roll.

The wire has a consequence written into PTS069 D rather than the marketing copy. The blanket is non-combustible to AS 1530.1. The mesh is not, because it has never been assessed: "The mesh has not been assessed to AS 1530.1, and testing the blanket/mesh assembly is not permitted by AS 1530.1." Under NCC 2022 steel including metallic coated steel may be used where a non-combustible material is required, through C2D10(5)(b). Bradford then adds the line that decides jobs: "NCC 2019 does not list this exemption." One roll answers differently on a 2019 job and a 2022 job. What non-combustible covers is in fire performance of insulation.

Choosing between the two wires has no published threshold behind it. No wire gauge, no aperture, no stitch pitch, no temperature limit for the galvanised coating. Stainless is the harsher environment option and the documents go no further.

One warning is unique to Fibermesh. All five statements open with the same line, isolate power before installation, but only PTS069 D adds that the steel mesh conducts electricity, and that neither it nor the conductive fasteners securing it should come into contact or close proximity with electrical wiring.

A selection path

1. Start at the hottest the surface gets, not the average. Take the lowest grade whose number sits above it. A flue peaking at 500 °C is a 650 product.
2. Then the shape. Flat and accessible: board, 1200 x 600 mm. Curved or in long runs: plain blanket, 4000 x 600 mm. Vessels, tanks, ductwork and large diameter pipe, where the wrap has to stay put on its own: Fibermesh.
3. Then the facing. Unfaced stone wool is not a water or vapour barrier. Where condensation control matters, Bradford's answer is the foil faced blanket, with the caveat below.
4. Then the thickness, from the R-value ladder rather than the grade.
5. Then the limitations. Every statement rules the product out of FRL applications and BAL-FZ, and out of exposed internal linings where a Group Number applies.

Where a drawing names a grade, a swap belongs with the engineer who wrote it. The evidence a lagging package has to carry is listed in specifying insulation for a tender.

The faced blankets, and the question nobody answers

Every Bradford service temperature sentence here begins with the same word: unfaced. The faced products have no published ceiling, and that matters to our own shelves. The three Fibertex 350 items we list at 4000 x 600 mm, codes 194450, 194448 and 194449 at 30, 50 and 75 mm, appear in CSR Bradford's current table as Blanket Foil Faced. So is code 465093, the item our Fibertex 450 variant calls "Blanket heavy duty faced" with no thickness, listed there at 75 mm. Our pages call both unfaced, and are being corrected.

So what temperature does a foil faced blanket carry? Bradford does not say. The nearest thing is a design note in the 2020 selector capping paper based, plastic based and glass woven facings far below 350 °C, with no figure for foil at all. It is written for HVAC design, not for this product. Bradford technical services is the only honest source, and the request should name the code.

What the facing is for is better documented. Bradford's 350 and 450 pages describe foil facing as adding durability and vapour control, the gap unfaced stone wool leaves open. No R-value is published for those codes either.

What Bradford does not publish

• Any R-value for Fibermesh. Not in PTS069 D, not on the web page, not in the selector, so mesh backed and plain blanket cannot be compared on published figures.
• Conductivity, and anything at working temperature. Every R-value is declared at 23 °C, which is not the condition the insulation is bought for. Nothing covers 400 or 700 °C.
• Mechanical properties. No compressive strength, no maximum service load, no shrinkage at temperature. The mechanical benefit of the higher density is claimed often and never quantified, so nothing says whether a board slumps on a vertical vessel.
• Acoustic data. No absorption coefficients and no NRC, although acoustic absorption is claimed on Bradford's pages and ours.
• Square metres per pack for the 820 strip. PTS068 J gives 45 linear metres and 60 pieces. Bradford's web table prints 0.17 m2 per pack, the area of one strip.

The absent figure with the widest reach is a fire resistance level. There is none, and every statement says so. That reaches our own Fibertex 820 Strips page, whose search description still offers the strips for fire dampers and acoustic baffles. PTS068 J rules code 16356 out of FRL applications and publishes no acoustic figure, so that line is coming out.

Where the documents disagree

Bradford has more than one current statement for some of these products, and they part company in four places.

• The datasheet we serve does not cover what we sell, on two products. Our Fibertex 350 and 450 listings link PTS165 B and PTS166 C, whose code tables carry only the newer 49xxxx range. A customer downloading our datasheet cannot find the item they bought. PTS065 E carries our four Fibertex 350 board codes and PTS066 F carries six of the seven 450 codes, so changing the linked file fixes most of it. It does not fix all of it: the four foil faced 4000 x 600 items, codes 194450, 194448, 194449 and 465093, are in no Bradford statement read here, and no R-value is published against any of them.
• Two R-values for one thickness. PTS066 F declares the 450 at 50 mm as R1.45, PTS166 C declares R1.40. The 350 splits the same way: R2.15 and R2.80 at 75 and 100 mm in PTS065 E, R2.0 and R2.75 in PTS165 B. Pack counts differ too, 2 pieces and 1.44 m2 against 3 and 2.16 at 100 mm.
• Fibermesh roll coverage. PTS069 D prints 3.8 m2 per piece for the 50 mm roll at 5 m x 600 mm. Bradford's web table and our catalogue say 3.0, and 5 m x 0.6 m is 3.0.
• Fibermesh 450's temperature. Bradford's current page covers both grades with one 650 °C line and our page repeats it. The 2020 selector splits them, 450 °C for the 80 kg/m3 grade. Treat the 450 as a 450 °C product and buy the 650 if the plant runs hotter.

Ask for a number that carries risk in writing, against the code being bought rather than the product name, as commercial versus residential specification sets out.

Frequently asked questions

Sources

General product information from the manufacturer's documents, read on 23 September 2026. It does not decide a lagging design, a thickness calculation or a compliance pathway, which belong to the engineer or certifier for the plant. Where two Bradford documents disagree, both figures are shown. Bradford changes specifications and codes without notice, so confirm the current statement against the product code before ordering.