Graphite EPS vs Mineral Wool: The 2026 Facade Guide

Two declarations decide this comparison, and they do not declare the same list of properties. Graphite EPS insulation boards are declared under EN 13163, ROCKWOOL mineral wool insulation under EN 13162, and the two standards ask their manufacturers for different characteristics — which is why a specifier reading them side by side finds figures on one side and blanks on the other.

This guide compares the two materials on what their own declarations of performance actually carry: thermal conductivity, declared resistance per thickness, reaction to fire, tensile and compressive classes, vapour and water behaviour. Where a property is declared NPD — no performance determined — that is stated as a blank rather than filled from a typical range, because a blank is what a specifier will find when the paperwork is checked.

What Decides the Graphite EPS and Mineral Wool Choice in 2026

The graphite EPS vs mineral wool 2026 UK decision turns on declared figures rather than reputation: 0.032 W/mK against 0.035 W/mK to EN 13163 and EN 13162, which moves wall thickness by one step on the ladder.

That thermal gap is narrower than the trade usually assumes, and it is rarely the deciding factor. Four constraints do more work, and it pays to identify which one is binding before either material is priced. Renders World supplies both routes, so the honest starting point is that neither is the default.

• Building height and use — above a defined threshold this stops being a comparison and becomes a legal restriction, covered below.
• Declared resistance against available depth — how much projection the reveals, sills and eaves can absorb before detailing has to be redesigned.
• Which properties the project needs declared — a compressive or water-absorption figure exists on one of these declarations and not the other.
• Vapour behaviour of the substrate — whether the wall behind depends on outward drying, which matters most on pre-1919 solid masonry.

Graphite EPS: What the EN 13163 Declaration Carries

The graphite façade board stocked here is Genderka EPS 032 Fasada Extra, declared to EN 13163:2012+A1:2015 with the designation T1-L2-W2-Sb2-P5-BS75-DS(N)2-DS(70,-)2-TR80. Graphite is added to the expanded polystyrene bead to cut radiative transfer through the cell structure, and the declared conductivity that results is λ_D 0.032 W/mK.

Resistance is declared per thickness rather than calculated, and the declared row is the one that belongs in a compliance file. The table gives 3.10 m²K/W at 100 mm, where dividing 0.100 m by 0.032 W/mK returns 3.125 — rounding that always favours the number nobody declared. The U-value calculation method for wall insulation thickness sets out how a declared row enters a full build-up, and why no board on its own carries a U-value.

• Reaction to fire: class E, declared for the board. A rendered wall is assessed as an assembly on its own evidence and does not inherit it.
• Tensile strength perpendicular to the faces: TR80, ≥ 80 kPa — the class that covers handling and installation as well as pull-off under the reinforced layer.
• Bending strength: BS75, ≥ 75 kPa, which is what lets a large board be carried and offered up without cracking across the middle.
• Compressive stress at 10% deformation: NPD. No value is declared, so none is published here — a point that matters at plinths and paved perimeters.
• Water absorption and water vapour transmission: NPD. The declaration determines neither, so this board supports no vapour or absorption figure at all.
• Tolerances T1 and W2 — thickness ±1 mm and width ±2 mm, tight enough for butt joints to close cleanly along a long elevation.

One reading trap is worth naming: W2 in that designation string is a width tolerance, not a water class. Nothing on this declaration supports a water-absorption claim in either direction.

Stone Wool Slabs: What the EN 13162 Declaration Carries

The stone wool slabs stocked here are ROCKWOOL FRONTROCK PLUS, declared under RW-CEE-DoP-0238/BCM/23/w1, and FRONTROCK SUPER under RW-CEE-DoP-0237/BCM/23/w1, both to EN 13162:2012+A1:2015 from Cigacice under notified body 1023. Plus declares λ_D 0.035 W/mK and Super 0.036 W/mK, so the premium-sounding name buys construction rather than a better thermal number.

Where these declarations are unusually complete is everything other than conductivity. Plus declares 2.25 m²K/W at 80 mm from its resistance table, and alongside it a full set of classes that the polystyrene declaration leaves blank.

• Reaction to fire: Euroclass A1 to EN 13501-1, declared for the slab, with durability of that classification declared A1 on the grounds that the organic content cannot increase over time.
• Compressive stress at 10% deformation: CS(10)20, 20 kPa — a declared figure where the EPS board has none, which is the answer whenever a specification demands one.
• Tensile strength perpendicular to the faces: TR10, 10 kPa, an eighth of the polystyrene board's class, so bonding coverage and fixing discipline carry more of the load.
• Water vapour diffusion resistance factor: MU1 — a factor of 1, about as open to outward drying as a solid material gets.
• Water absorption: WS 1.0 kg/m² short term and WL(P) 3.0 kg/m² long term, so an exposed boarding window is a managed condition rather than an unknown.
• Dimensional stability DS(70,90), stable at 70 °C and 90% relative humidity, meaning the slab is not the source of movement at board junctions.

Two properties the trade expects to find are absent from both declarations. Neither declares a density, and the stone wool declaration returns NPD for sound absorption and for the airborne sound insulation index — so no decibel advantage can be quoted from it, however often one is repeated elsewhere.

Graphite EPS and Mineral Wool Compared on Declared Figures

Every cell below is copied from the declaration named in its column heading, at that document's scope: a board or a slab as manufactured, never a rendered wall. Blanks are blanks.

What the Thickness Premium Actually Costs in Millimetres

Reading the two declared resistance tables against each other gives the depth penalty directly, without a U-value calculation in between. The polystyrene board's 3.10 m²K/W at 100 mm is matched by the stone wool table at 110 mm, also 3.10 — a premium of 10 mm. Further up, EPS 6.25 m²K/W at 200 mm is matched by stone wool at 220 mm, also 6.25 — a premium of 20 mm.

So across the range a UK retrofit actually specifies, the penalty is one step on the thickness ladder, 10 to 20 mm, not the 20 to 40 mm the market repeats. On most elevations that is one bead depth and a slightly deeper sill projection rather than a redesign, which reframes the whole decision: if height, a declared compressive figure or vapour openness points to stone wool, the depth cost of following that pointer is smaller than expected. The 110 mm and 120 mm rows of the polystyrene table both read 3.40 m²K/W in an otherwise rising series, so neither is used here or anywhere else.

Where Regulation Removes the Choice Above 18 Metres

At a certain height the comparison ends. Regulation 7(2) of the Building Regulations requires that materials becoming part of an external wall of a relevant building are of European Classification A2-s1, d0 or A1. A relevant building is defined there as one with a storey at least 18 metres above ground level that contains one or more dwellings, an institution, or a room for residential purposes, measured to the top of the floor surface of that storey.

A class E board does not meet that requirement, so on those buildings a non-combustible slab is the specification rather than the preference. Two details in the same regulation are worth carrying into a design:

• Insulation below ground level, or up to 300 mm above it, is excluded from paragraph (2) — which is why plinth detailing is treated separately, as the below-DPC and plinth board comparison works through.
• Relevant metal composite material is prohibited in the external wall of any building, at any height, under paragraph (1A).

Below that threshold the regulation leaves the choice open, and it becomes a fire strategy question for the specific building under current Approved Document B guidance rather than a rule that can be quoted from a material sheet. The published class belongs to the board or the slab; a finished rendered wall carries its own evidence, assessed as an assembly.

How the Choice Changes the Adhesive, Fixings and Render

Whichever material wins, it changes the four layers around it, which is where a switch late in a project costs money. Both boards belong to the same external wall insulation silo and stack in the same order, and the EWI build-up layer sequence is the reference for how they sit together.

• Adhesive is not interchangeable. The graphite board's data sheet permits only products dedicated to grey graphite boards — cement-based adhesives, polyurethane foam adhesives or water-dispersion bitumen compounds. Stone wool needs a cementitious product, because open fibre gives foam nothing to key into; both routes are covered by the EPS adhesives basecoats range.
• Sequence differs on the polystyrene side. Its sheet asks for the bonding face to be abraded immediately before bonding, and for mechanical fixing no earlier than 24 hours after — an overnight break to plan around, not an afternoon push.
• Fixing counts come from the system designer. With a declared tensile class of 10 kPa against 80 kPa, the stone wool build-up leans harder on bonding coverage and fixing layout; how that number is arrived at is set out in the fixing pattern and spacing guide.
• Protect grey boards from sunlight. The steel-grey faces must be shielded from direct sun in storage and on the wall, briefly and over time, and opaque sheeting on the scaffold handles it.

On vapour the asymmetry is the whole point. The slab declares MU1, a diffusion resistance factor of 1, so the insulation layer barely resists outward drying; the polystyrene board declares nothing for vapour transmission, so it supports no figure to model with. Where a solid wall depends on drying outward, that is decisive — the condensation risk assessment method for external insulation covers how the check is run, and the interlayer condensation physics shows what the layers do between them.

Choosing Between the Two on a 2026 Project

Key Takeaway: The thermal gap is one step on the thickness ladder — 10 mm at 100 mm, 20 mm at 200 mm — while the declaration gap is much wider. Stone wool declares compressive strength, water absorption, vapour resistance and Euroclass A1; the graphite board declares none of the first three and class E for the fourth, but eight times the tensile class and 0.032 W/mK. Specify against whichever declaration answers the question your project is being asked.

The eps or mineral wool for facades UK question resolves cleanly once the binding constraint is named. Above 18 metres on residential stock the regulation names it for you. Below that, the graphite board suits low-rise work on modern non-porous masonry where depth and repeatability matter, and the 100 mm graphite board at 3.10 m²K/W is the depth most solid-wall work settles on.

Stone wool suits any project needing a declared class the polystyrene declaration leaves blank, any wall depending on outward drying, and any fire strategy that wants non-combustible insulation regardless of height — the FRONTROCK PLUS 80 mm slab at 2.25 m²K/W is the full-elevation thickness. This insulation material comparison for 2026 was reviewed in August 2026 against both declarations; material prices sit on the two collection pages, and Renders World quotes material and installed cost separately so a specification change can be priced honestly rather than absorbed. Renders World holds both routes with matched adhesives and basecoats, so pivoting between them does not mean changing supplier.

Written by Mariusz Saja. Technically reviewed by Rafał Wyrzykowski. Last reviewed Aug 2026.

Graphite EPS and Mineral Wool Questions Answered

How much extra thickness does stone wool really need?

Read from the two declared resistance tables, 10 to 20 mm across the practical range. The graphite board's 3.10 m²K/W at 100 mm is matched by the stone wool table at 110 mm, and its 6.25 m²K/W at 200 mm is matched at 220 mm. That is one step on the ladder, which usually means a deeper sill projection rather than redesigned detailing.

Which board is stronger?

It depends entirely on which strength, and the answer is not the one the market assumes. The stone wool slab declares compressive stress at 10% deformation as CS(10)20, 20 kPa, while the graphite board declares that property NPD — no figure at all. Reverse the question to tensile strength perpendicular to the faces and the polystyrene board declares TR80, ≥ 80 kPa, against the slab's TR10, 10 kPa.

Can the two be mixed on one elevation?

Mixing is common practice where a fire strategy calls for non-combustible bands, but it is a system decision rather than a materials one. The build-up needs the system holder's detailing and warranty to cover the hybrid, a render finish compatible with both substrates, and a junction detail at every material change. Neither declaration says anything about combining products, so that evidence comes from the system specification.

Does either board suit work below damp-proof course?

Neither of these two declares a water-absorption or compressive figure suited to it — the graphite board declares both NPD, and the slab is a façade product. Regulation 7(2) separately excludes insulation below ground level, or up to 300 mm above it, from its classification requirement, which is a further sign that the plinth is specified as its own zone with a board declared for the duty.

Is stone wool measurably better acoustically on a facade?

Not from anything these declarations carry. The stone wool declaration of performance returns NPD for both sound absorption and the airborne sound insulation index, and the polystyrene declaration returns NPD for the impact sound index, so no decibel figure for either product is available to publish. Where acoustics drive a specification, that evidence has to come from a tested wall assembly rather than a board.

Does Euroclass A1 make the finished wall non-combustible?

Classification belongs to the thing that was tested, and here that is the slab under EN 13501-1. An external wall finished with an organic render is assessed as an assembly on its own evidence under current Approved Document B guidance, so the slab's class is quoted against the slab and its declaration number rather than carried up to the façade.