Swisspearl Windstopper Extreme

Swisspearl Windstopper Extreme is a wind barrier board for ventilated exterior wall assemblies. It is a build board that sits behind the final façade and is not a finished color line. The US listing places it in the commercial rainscreen substrate group, behind the insulated wall and rainscreen systems that use Swisspearl panels as the outer layer.

Its technical sheet, dated 08-2025, also covers Windstopper Connect, so the sheet carries three product columns: WSE 4.5 mm, WSE 9 mm and WSC 9 mm. Extreme refers to the first two.

The board consists of gray cement and limestone filler, reinforced with a specially selected fiber material. The fiber can absorb and release moisture without affecting the durability, strength or performance of the board. The surface is uncoated fiber cement and the board comes in two natural colors.

It resists rot and fungal growth and withstands considerable fluctuations in weather and climate conditions. The board is non-combustible.

Extreme has a very low vapor transmission resistance, which lets moisture from inside the building pass through. Insulation can be placed directly against the inner side of the board.

Values at 4.5 mm and 9 mm are as follows.

• Z-value: 2.1 GPa m² s/kg at 4.5 mm and 2.7 at 9 mm.
• Vapor transmission resistance: 15600 s/m at 4.5 mm and 19700 s/m at 9 mm.
• Sd: 0.41 m at 4.5 mm and 0.50 m at 9 mm.
• Resistance factor μ: 87 at 4.5 mm and 82 at 9 mm.
• Vapor transmission: 8.3 USPerm at 4.5 mm and 8.0 USPerm at 9 mm.

Air permeability (EN 12114) is 0.05 m³/m² h Pa or less. Water impermeability (EN 12467) is recorded as no water drops.

• Thicknesses: 4.5 mm and 9 mm.
• Widths in the US listing run from 35.43 to 106.30 in, and lengths from 35.43 to 118.11 in.
• Tolerances (EN 12467, Level 1): thickness +/- 0.6 mm at 4.5 mm and +/- 0.9 mm at 9 mm; width +/- 3 mm between 600 and 1000 mm and 0.3 percent of width between 1000 and 1600 mm; length +/- 5 mm.
• Dry density: at least 1400 kg/m³ at 4.5 mm and 1300 kg/m³ at 9 mm; production averages are 1554 and 1375 kg/m³.
• Average weight including 10 percent moisture: 7.7 kg/m² at 4.5 mm and 13.6 kg/m² at 9 mm.

The flexural modulus along the grain is 16.9 GPa (4.5 mm) and 5.5 GPa (9 mm) at ambient conditions, and 7.6 and 2.3 GPa when wet. Across the grain it is 16.1 and 12.9 GPa at ambient conditions, and 8 and 5.8 GPa when wet.

Bending strength along the grain is 17.5 MPa (4.5 mm) and 13.2 MPa (9 mm) at ambient conditions, and 7.9 and 5.5 MPa when wet. Across the grain it is 22.1 and 16.4 MPa at ambient conditions, and 11 and 7.4 MPa when wet.

Thermal conductivity λ10 is 0.32 W/(mK) and the expansion coefficient is 0.01 mm/m °C. Frost resistance is a minimum of 100 cycles with an average R above 0.75. Water absorption is 19.9 percent at 4.5 mm and 21.3 percent at 9 mm, and moisture movement at 30/90 percent RH is 0.55 and 0.42 mm/m.

At 4.5 mm the sound reduction values are Rw 29 dB, Rw + C 28 dB and Rw + Ctr 25 dB. At 9 mm they are 32, 31 and 28 dB.

Reaction to fire (EN 13501-1) is A1 at both thicknesses. The fire protection classification (EN 13501-2) is not applicable at 4.5 mm. At 9 mm it is K1 10 and K2 10, and K2 30 for an assembly of two layers of 12 mm Multi Force fixed directly to the substrate with the 9 mm Windstopper Extreme facing the fire exposure. The category and class (EN 12467) is NT A1 l.

Installed to the Swisspearl installation instructions, Windstopper Extreme and Windstopper Connect can function as a temporary façade for up to 12 months.

The US product page gives the screw for steel framing as the SCR-S 4.2 by 30 millimeter universal screw and for wood framing as the SCR-W 3.9 by 38 millimeter universal screw, with no predrilling required in the listed application.

Windstopper Connect, covered on the same sheet, is a 9 mm board with tongue and groove on all four edges. A non-hardening butyl sealant is applied in the short groove and a water-repellent surface treatment is applied to the front. Its standard size is 600 by 1500 mm.