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25mm Aluminium Black Foil Faced 2 Sides RS45 Slab (pack of 20)

25mm Aluminium Black Foil Faced 2 Sides RS45 Slab (pack of 20)
25mm Aluminium Black Foil Faced 2 Sides RS45 Slab (pack of 20)
  • 25mm Black Foil Faced x2 Sides Knauf RS45 Insulation Slab A1 Class
  • Class ‘O’ to the Building Regulations and Class A1 fire performance
  • Density of 45kg/m3 with an excellent thermal and acoustic properties
  • Provides from 30 up to 240 minutes of fire protection (x2 Foil Faced RS45)
  • Double Sides Black Foil Faced Slab accumulates heat on one side of the slab
Estimated delivery:
In Stock
£ 624.00
Ex VAT: £ 520.00
  • Brand: Knauf®
  • Model: 25mm RS45 Black Foil Faced x2 Sides
  • Dimensions: 1,200mm x 600mm x 25mm
  • SKU: 25mm RS45 Black Foil Faced x2 Sides
  • Product code: P3686
  • MPN: 25mm RS45 Black Foil Faced x2 Sides

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25mm Black Foil Faced Two Sides Knauf RS45 Slab is a semi rigid rock mineral wool black foil backed on both sides insulation slab with an excellent class A1 fire performance.

Knauf RS45 Black foil backed on both sides slab provides outstanding fire, thermal and acoustic performance for both new build and refurbishment projects.

Black Foil Faced 2 Sides RS45 Insulation Slab is a fire-resistant insulation solution designed for concrete soffits and other applications where fire rating is crucial.

The black aluminium foil facings on both sides accumulate heat on one side of the board, unlike the aluminium silver foil that reflects the heat.

Black foil backed and faced insulation slab is less visible than the silver foil which is handy specially during the exposed and semi-exposed ceiling works.

Rocksilk RS45 Insulation Slab is an efficient insulation with a certified thermal conductivity of 0.035W/mK and manufactured with a density of 45kg/m3.

Black Foil Faced and Backed RS45 can be used as an insulation in partitions, soffits, timber and metal studs, and in between timber rafters and floor joists.

Knauf Insulation Slabs RS45 with black aluminium foil facings have excellent sound absorption characteristics providing high levels of sound reduction.

These odorless, non-hygroscopic, and rot proof slabs are free of CFCs and HCFCs and will not encourage the growth of fungi, mould or bacteria.

Knauf Insulation products made with ECOSE Technology contain no formaldehyde binder, dye or artificial colours.

RS45 Building slabs are also Zero ODP and Zero GWP which makes them more eco-friendly material.

Rocksilk RS45 black foil backed and faced slab is easy to cut and shape with a large bladed knife or saw.




Thickness: 25mm

Width: 600mm

Length: 1200mm

Pack Quantity: 20

Slab Coverage: 0.72m2

Pack Coverage: 14.40m2

Finish: Black foil faced two sides

Density: 45kg/m3 

R-Value: 0.70m2K/W

Thermal Conductivity: 0.035W/mK

Vapour Resistivity: 5.00MNs/g.m.

Surface Spread of Flame: Class 1 

Building Regulations: Class ‘0’ 

Fire performance: Euroclass A1 (non-combustible)


Black Foil Faced and Backed Knauf Rocksilk RS45 Features:

 · Easy to cut.

 · Easy to shape.

 · Free of CFCs and HCFCs.

 · Zero ODP and Zero GWP.

 · Rock mineral wool core.

 · Highly efficient insulation.

 · Black aluminium foil faced slab.

 · Black aluminium foil backed slab.

 · Fire-resistant insulation solution.

 · Excellent class A1 fire performance.

 · Designed mainly for concrete soffits.

 · Provides outstanding fire performance.

 · Manufactured with a density of 45kg/m3.

 · Providing high levels of sound reduction.

 · Provides outstanding thermal performance.

 · Excellent sound absorption characteristics.

 · Provides outstanding acoustic performance.

 · Certified thermal conductivity of 0.035W/mK.

 · Odorless, non-hygroscopic, and rot proof slab.

 · Provides from 30 up to 240 minutes of fire protection.

 · Suitable for both new build and refurbishment projects.

 · Suitable for  applications where fire rating is crucial.

 · Contain no formaldehyde binder, dye or artificial colours.


Knauf RS45 (Black Foil Faced Two Sides) Insulation Slab Installation Guidelines:

 · Black Foil Faced and Backed Slab can be rapidly installed onto rectangular and square steel ductwork using a combination of stud welded pins and steel washers.

 · All board abutments and cross joints must be covered with aluminium foil tape.

 · Black Foil Faced on both sides Slab is easily cut with a hand saw or alternatively a circular/table saw.

 · The top and bottom slabs should be cut 10mm wider than the width of the duct to ensure a tight cross joint with the side slabs.

 · The side slabs should be cut to the height of the duct (H) + 2 x the insulation thickness.

 · When installed within horizontal applications the top boards do not require any stud welded pins and are simply positioned onto the duct with all board joints bonded with the glue.

 · Board joints must be covered using foil tape.

 · The side wall slabs are installed using stud welded pins with 350mm maximum centres along the length of the duct and 400mm centres across the depth.

 · Side wall slabs must overlap the top and bottom boards.

 · All cross joints must be bonded with the glue.

 · Ensure that there is a strong bond between the welded pin and the duct, always ensure that the welded pin is sufficiently isolated from the foil surface of the insulation during welding.

 · Install the base slabs with stud welded pins at a maximum of 350mm centres along the length of the duct and 300mm centres across the width of horizontal ducts and 450mm across the width of vertical ducts.

 · Where the Black Foil Faced Two Sides Slab bypasses a flange, drop rod hanger or both, cut a notch into the insulation.

 · The insulation can easily be cut with a sharp knife or hand saw.

 · All board joints must be bonded with the glue.

 · A joint in the Black Foil Faced and Backed Slab must be accommodated at the centre point of the aperture.

 · Before applying the u-profile to the Black Foil Backed and Faced Slab, slits must be cut into the insulation to allow the profile sides to penetrate the insulation.

 · The u-profile can be attached to the ductwork using 100mm self-tapping screws.

 · Approx. 4no. to the top and bottom slabs and 2no. to the vertical slabs.

 · Once the u-profiles have been applied an insulated collar must be installed around the perimeter of the aperture.

 · The collar can be simply cut from the Black Aluminium Foil Faced Two Sides Slab.

 · Fix the collars in place with the glue.

 · Use nails to temporarily hold the collars in place whilst the glue cures.

 · Foil tape can be used to cover any exposed edges of the collars.

 · Maintain a 30mm gap between the ductwork and floor structure.

 · Secure the duct to the floor structure using 4no. 50 x 50 x 45 x 2.5mm galvanised steel angles to both sides of the aperture.

 · The angles can be fixed using 2no. 3.2 x 25mm self-tapping screws.

 · Alternatively, the duct can be secured with a 40 x 40 x 3mm L profile.

 · The length of the L profile should be equal to the width of the duct and installed to both sides (duct width).

 · Elbows can be protected by cutting the Black Foil Faced 2 Sided Slab into fan shaped segments.

 · Alternatively v-shaped slits can be cut into the back of the Black Foil Faced 2 Sides Slab allowing it to wrap around the elbow.

 · Fill the v-shaped channels with the glue before applying to the duct and use nails to temporarily hold the insulation in place whilst the glue cures.

 · Black Foil Faced and Backed Slab can be cut and positioned within a steel frame to form a removable cover in the location of the steel access hatch.

 · The insulated cover can be attached to the duct using 4no. M8 threaded rods ensuring the rods are secured on both sides of the duct.

 · The cover is then fixed to the rods using steel M8 nuts and washers.

 · The thickness of insulation should be appropriate to the fire resistance required.


*Further information may be found in our Downloads section.

Fairly easy access to all PDF files.

Datasheet ǀ Declaration of Performance - DoP ǀ BBA Certificate ǀ Installation Guide ǀ Certificates ǀ Brochure ǀ SPEC Sheet 

*Special Product - Non returnable cancelable.

Board covarage 14.40 m2
Colour Brown Core ǀ Black Foil Facings
Density 45kg/m3 
Length 1200mm
Material Rock Mineral Wool ǀ x2 Black Aluminium Foil
Pack Coverage 14.40m2
Pack Quantity 20
R-Value 0.70m2K/W
Size 25mm x 600mm x 1200mm
Thermal Conductivity 0.035W/mK
Thickness 25mm
Width 600mm
Fire Classification Euroclass A1
Vapour Resistivity 5.00MNs/g.m.
Slab Coverage 0.72m2
Fire Reaction Non-combustible
Building Regulations Class ‘0’ 
Coverage 14.40m2
Finish Black foil facings on both sides
Quantity 20
Shipping method Articulated Vehicle ǀ Courier
Applications Soffit ǀ Floor ǀ Wall ǀ Roof ǀ Partitions
Foil faced Both sides
ECOSE Technology Yes
ETA Notification Yes
Features Black aluminium foil faced and backed slab class A1
Manufacturer Knauf Rocksilk®

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We deliver insulation materials to Mainland UK only. Deliveries to Highlands, Northern Ireland, Isle of Wight etc.. might be possible at additional cost.
We offer free delivery on most of the orders above £300 (excluding VAT) (except special products - shipping cost via courier - products marked ''Request A Quote'')

Delivery of some insulation materials might be extended due to the current situation (Covid-19, stock shortages, allocations).
If you need materials quickly please contact us - we will do our best to help you source materials needed.

We do not deliver on weekends and bank holidays. Sometimes we can deliver on Saturdays - please check with us before placing the order.
If you need any further information please contact us tel. 02081910776

We can help to calculate price per m2 or linear meter (one meter in length) cost, please just contact us via phone 02081910776, email or live chat. Alternatively, you can work it out yourself quickly and easily: to get cost per meter square please divide price shown in orange area by ''Required area (m2)'' Example price of £28.80 divided by board coverage 2.88m2 = cost of £10.00 per m2.


No matter whether you choose a local installer or a national company, there’s a few tips to help you find the right installer for your home insulation improvements, such as asking for recommendations and making sure that they’re part of a certification scheme. This makes sure that they have the right skills and standards of workmanship to carry out the installation, and you can be sure that they know exactly what they are doing.


1. Thermal inspection picture in portfolio

It’s worth seeing a installer’s previous work. There’s no harm asking if you can see any properties nearby that they’ve installed insulation in. Best way would be to see Infrared Thermal Imaging Inspections. Thermal cameras spot small, but key changes in temperature in different areas of a house, identifying problematic areas that the human eye never could and some that a visual inspection could only hypothesize.

2. Reviews

Along with checking recommendations and previous work, finding reviews online can often be a great way to find out if they provide a good service or not. However, it’s best not to solely rely on reviews you may find or review websites, as there’s no controlling who writes them.

3. Compare prices

Comparing prices will also ensure companies can’t take advantage of you and give you a fair price. 

4. Word of Mouth

The best way to find a great insulation installer is through recommendations. Make sure you ask friends and family. They will most likely give you their honest opinion and can tell you from first hand experience.


Whether you require a wall, cladding, external wall, loft or floor insulation fitted, you can find and hire your local insulation installers from popular UK web pages. A simple internet search will return thousands of potential installers near your area.



We are the stockist of construction materials and related products for both trade and DIY from most recognizable brands in the UK like Cordek, RCM, Promat, Rockwool, Isover, Celotex, Xtratherm, Ursa, Low-E, Cedral, Kingspan, Dufaylite, British Gypsum, K-rend, Ecotherm, Iko enertherm, Kay-Metzeler, Terrawool to allow you to complete your insulation job on time at competitive prices and the highest standards.


Whether you are a large company or a DIYer, if you need a large amount of insulation materials, we can offer quantity discounts at the best prices. Please contact us and our friendly customer service will try to find the best and cheapest solutions for you. We value your time and we will try to deliver the products as soon as possible at a reasonable price to your construction site or house. The UK's leading insulation supplier near you and your needs. Price List available upon request.
25mm Aluminium Black Foil Faced 2 Sides RS45 Slab (pack of 20)
25mm Aluminium Black Foil Faced 2 Sides RS45 Slab (pack of 20)
£ 624.00