Calcium silicate insulation is a mineral board that architects mostly meet as internal insulation for solid masonry, where the facade has to stay as it is. Two product families appear under the name: Xella's Multipor, the board most people search for, and the calcium silicate boards Calsitherm makes and Redstone sells. They share a chemistry and an application but not their numbers, so this profile keeps each maker's documents apart.
We read European Technical Assessments, two EPDs, data sheets, an Xella brochure and two simulation studies. The Xella and Redstone documents are German and Austrian; where the original is German we say so. For the lime-based finishes these boards are plastered with, see lime plaster and clay plaster; for a plant-based internal option see wood-fibre insulation.
What is calcium silicate insulation, and how do Multipor and Redstone boards differ?
Xella's data sheet describes Multipor as a solid, mineral, monolithic insulation made of calcium silicate hydrates, with lime, sand, cement, water and a pore-forming agent, and a porosity of about 95 % by volume.[2] Its EPD is more specific: the boards are autoclaved aerated concrete-based, aluminium paste is the pore former (the metal reacts in the alkaline mix and releases hydrogen that makes the pores), pores are usually 0.5 to 1.5 mm, and steam curing forms calcium silicate hydrates corresponding to the mineral tobermorite.[3] The ETA describes the same product as made of quartz powder, calcium hydrate, cement and aggregates.[1]
The Redstone boards are made differently. According to the ETAs they are factory-made boards of calcium silicate and cellulose fibres, autoclaved, uncoated, with one side optionally slotted.[5][8] Calsitherm's EPD puts the cellulose at under 0.6 % by volume and lists microsilica among the raw materials, which it models as a secondary raw material without production impacts.[9] The ETAs name Calsitherm Silikatbaustoffe's Paderborn plant as the manufacturing site, and redstone GmbH & Co. KG as the ETA holder.[5][8] A third brand, einzA Schimmelschutz, holds its own ETA for boards of calcium silicate and cellulose fibres. Its April 2025 version named the same Calsitherm plant and gave the same λD of 0.059 W/(m·K) and 180–187 kg/m³ as Redboard pro; the version of 17 September 2025 that replaces it names the plant only as "Werk 3" and declares λD 0.075 W/(m·K), 235–253 kg/m³ and 1,500 kPa, the Redboard basic and Clima Solid values. We list einzA as a brand of the same board family rather than a separate maker, but the current ETA no longer names the plant, so that is our reading of the earlier version.[11]
What do the ETAs and data sheets declare for conductivity, density and strength?
Both makers declare through a European Technical Assessment issued by Deutsches Institut für Bautechnik under EAD 040012-00-1201. The ETAs give declared λD at 23 °C and 50 % relative humidity and say the design value is to be set under national provisions.[1][5] The rated values in the table come from the manufacturers' data sheets, not from the ETAs. DIBt's download page lists ETA-05/0093 of 30 October 2024, ETA-19/0559 of 30 October 2019 and ETA-24/1060 of 25 October 2024 as the latest versions, and gives no expiry date for any of them (checked 19 Oct 2026).[1][5]
| Product | Manufacturer | λD(23/50) declared in the ETA, W/(m·K) | Rated λ in the manufacturer's data sheet, W/(m·K) | µ (EN 12086) | Density, individual values (EN 1602), kg/m³ | Mean compressive strength (EN 826), kPa | Src |
|---|---|---|---|---|---|---|---|
| Multipor insulation board M4 (TIPwall) | Xella Baustoffe GmbH | 0.040 | 0.042 (walls, 60 mm and thicker) | 2 | 85–95 | ≥ 200 | [1][2] |
| Multipor insulation board M3 | Xella Baustoffe GmbH | 0.043 | 0.045 | 3 | 100–115 | ≥ 300 | [1][2] |
| Clima Redboard pro | redstone GmbH & Co. KG | 0.059 | 0.062 | 3 | 180–187 | 1,000 | [5][6] |
| Clima Redboard basic | redstone GmbH & Co. KG | 0.075 | 0.080 (data sheet status 12/12/2019) | 3 | 235–253 | 1,500 | [5][7] |
| Clima Solid | redstone GmbH & Co. KG | 0.075 | not stated in the documents we read | 3 | 235–253 | 1,500 | [8] |
Read the table as four different products, not as a ranking: the boards differ in density, binder and cellulose content, and the ETA strength values are mean values from which individual results may fall up to 10 %.[1][5] Xella also declares M0 (λD 0.047, µ 5, 110–125 kg/m³, ≥ 350 kPa), M2 (0.045, µ 3, 100–115 kg/m³, ≥ 350 kPa) and M4 light (0.040, µ 2, 75–84 kg/m³, ≥ 150 kPa) grades.[1] Xella's EPD gives a tensile strength of 0.08 N/mm², and its data sheet gives a specific heat capacity of 1.3 kJ/(kg·K).[3][2] The Redstone ETAs list bending strength, tensile strength, point load and porosity as "no performance assessed".[5][8]
How do the boards handle vapour, water, alkalinity and mould?
Vapour and sorption
The µ values are in the table: 2 to 5 for Multipor depending on grade, 3 for the Redstone boards.[1][5] Calsitherm's EPD gives 3 to 6 for its whole range of calcium silicate boards, including denser grades, so it is a wider statement than the ETAs.[9] For sorption the documents give different figures: the Multipor ETA gives a mass-related moisture content of 0.032 kg/kg at 23 °C and 80 % relative humidity, while Xella's EPD and data sheet state "< 6" and "≤ 6" mass-% at the same condition (0.032 kg/kg is 3.2 mass-%, inside that bound, so the documents differ in precision rather than direction).[1][2][3] The Clima Solid ETA gives 0.018 kg/kg (1.8 mass-%), whereas Calsitherm's EPD gives about 7.5 mass-% for the product family; we show these as printed and do not reconcile them.[8][9]
Water absorption and capillary activity
The Multipor ETA gives water absorption of ≤ 2 kg/m² (EN 1609, method B) and ≤ 3 kg/m² (EN 12087, method 1B; ≤ 4 kg/m² for M0), and Xella's EPD lists water-soluble methyl silicone hydrophobing agent among the additives.[1][3] Xella's brochure nonetheless describes the system as vapour-open and capillary-active, with condensate taken up in the board and returned to room air; we did not find a capillary absorption coefficient in the Xella documents we read.[4] Redstone's data sheets state water absorption coefficients of 51 kg/m²√h (Redboard basic) and 46 kg/m²√h (Redboard pro), while the Redstone ETAs assess no water absorption.[6][7][5] These Xella and Redstone figures come from different tests and are not comparable.
pH and mould
Redstone's Redboard pro data sheet gives a pH of about 10.[6] Calsitherm's EPD ties the boards' resistance to rot, insects and rodents to their alkaline pH, and Xella's EPD says the boards react slightly alkaline on contact with water.[9][3] Redstone describes its boards as mould-resistant and Xella's data sheet as having an inhibitory effect against fungi and microorganisms; these are manufacturer statements and we did not open a mould test report.[6][2]
How are the boards installed on an internal wall?
Xella's brochure (issued by Xella Porenbeton Österreich, edition 06/2025) describes the Multipor TIPWall system: boards bonded fully to the wall with a lightweight mortar, a hemp-felt decoupling strip at adjoining elements, butt and bed joints closed and mortar-free, a reinforcement layer with mesh, and a 2–3 mm top coat of the system mortar or a lime smoothing coat, and a finish such as vapour-open silicate interior paint. Doweling is not generally needed but is required on non-load-bearing substrates, on crumbling old plaster treated with silicate consolidants, and under tiles, which Xella limits to 25 kg/m² including adhesive.[4] Xella's EPD gives about 3.5 kg/m² of mortar and says the boards are cut with band saws or by hand with carbide saws or cutters; the documents differ on the mortar standard, with the EPD citing EN 998-2 and the brochure's table listing a lightweight mortar to EN 998-1.[3][4]
Redstone's data sheets describe a clean, load-bearing, tension-free mineral substrate, full-surface bonding with a notched trowel (at least 10 mm), joints no wider than 3 mm bonded or meshed, a primer, then levelling compound or lime smoothing coat and only breathable paints. They call for plugs at two per m² in rooms higher than 3.50 m and four per m² on ceilings and sloped ceilings or where loads such as tiling are expected, and a special sulphate-resistant adhesive on gypsum-containing substrates.[7][6] Xella instead says gypsum plaster is to be removed completely.[4] Calsitherm's technical notes advise against wallpaper and paste because they restrict the vapour-open, capillary-active function, and ask for dust protection when boards are cut indoors.[10]
How much carbon do the EPDs declare?
Both makers have an IBU EPD under EN 15804+A2, and both appear on the IBU's published EPD list (checked 19 Oct 2026). The two use different declared units and scopes, so the table keeps them apart and converts nothing.
| EPD | Declared unit | Modules declared | GWP-total A1–A3, kg CO₂e | GWP-fossil / biogenic A1–A3, kg CO₂e | Other as printed | Src |
|---|---|---|---|---|---|---|
| Multipor mineral insulation board, Xella Baustoffe GmbH, EPD-XEL-20250256-IBA1-EN (issued 11/04/2025, valid to 10/04/2030; German plants Stulln and Köln-Porz, 2023 data) | 1 m³ at an average 102 kg/m³ | A1–A3, A4, A5, B1, C1–C4, D | 123 | 122 / 0.279 | B1 (recarbonation, 95 % assumed): −26.7. Mortar not included. Reference service life ≥ 50 years. | [3] |
| Microporous calcium silicate insulation, Calsitherm Silikatbaustoffe GmbH, EPD-CAL-20240411-IBC3 (issued 22.11.2024, valid to 21.11.2029; Paderborn plant; covers Klimaplatte, Redboard, Clima Solid, Silca, Silcal) | 1 tonne at an average 259 kg/m³ (the range covers 170 to 550 kg/m³) | A1–A3, A5, C1–C4, D (A4 and B1 not declared) | about 1,400 (printed 1.4E+03) | 1,460 / −55.2 | Landfill scenario declared, C3 = 0. Reference service life 80 years. | [9] |
The figures cannot be set side by side. One is per cubic metre of a single product at 102 kg/m³, the other per tonne of an average across a wide density range, and the Calsitherm EPD cannot be converted to a specific board without that board's density. Insulation is also bought for thermal resistance, not mass. Xella's EPD says a comparison is only possible between EN 15804 datasets with the building context taken into account, and it excludes the adhesive mortar.[3]
On the carbon cycle, Xella's EPD declares a negative B1 value of −26.7 kg CO₂e, the recarbonation of reactive components, using a 95 % recarbonation rate cited to a 2022 source; it sits next to the 123 kg CO₂e of A1–A3 and we do not net the two.[3] Calsitherm's EPD text says the company compensates the CO₂ from its natural gas through certificates bought from its energy supplier; we do not net that against the declared figures either.[9]
What do the documents say about end of life?
Xella's EPD calls the boards fully recyclable, assigns waste code 17 01 01 and class II landfill disposal, and says there is currently very little possibility of reusing the boards after dismantling. Its recycling scenario (C3) is use as fill material, with 125 kg recycled and 129 kg landfilled per declared unit in the two alternative scenarios, which are not to be added.[3] Calsitherm's EPD calculates a landfill scenario and describes, in text only, reuse of boards that are neither glued nor plastered, grinding for use as a filler, substituting a pore-forming agent in brick manufacture and adding the ground boards to clay insulating plasters, where adhering lime adhesive and plaster need not be separated.[9] Internal-insulation boards are normally bonded and plastered, so the first of those routes is of limited use there; that is our interpretation, not a statement in the EPD.
What does independent research say about moisture risk?
We read two simulation studies at abstract level only. Freimanis and co-authors (2023) simulated a vapour-open, capillary-active calcium silicate system in cold climate with the Delphin software, using tested properties of 40 historic brick samples; temperatures behaved similarly across wall types while moisture behaviour differed greatly, and applying adhesive tended to reduce rain-event moisture spikes compared with the same samples without it.[12] Finken, Bjarløv and Peuhkuri (2016) simulated capillary-active internal insulation of several materials, 30 to 150 mm thick, on the solid brick wall of a historic Copenhagen dormitory; as summarised on the university portal, all variants showed critical relative humidity above 80 % without exterior protection, and façade impregnation against driving rain was needed for a moisture-safe result. The authors conclude that such insulation may be unsuitable for bare solid masonry in thin-walled multi-storey buildings in wet climates.[13] That second study is not specific to calcium silicate: its abstract lists calcium silicate alongside AAC and IQ-Therm systems.
When to specify it, and when not
Where the documents support it
Suits: solid mineral masonry · facades that must stay unchanged
Xella's brochure says internal insulation is often the only effective way to improve the thermal performance of a preserved or elaborately designed facade, and describes TIPWall as suited to listed buildings; this is the manufacturer's own claim.[4] Xella describes its system as vapour-open and working without a vapour barrier, and says this makes it more forgiving of detailing than vapour-retarding systems; Calsitherm's notes describe its Klimaplatte system as vapour-open and capillary-active.[4][10] The ETAs give Euroclass A1, with the Redstone caveat that A1 is only proved for boards without paints or coatings. Redstone's 2026 Redboard pro data sheet describes that board as primed on the room side, while ETA-19/0559 describes the boards as not coated; we show both and do not reconcile them.[1][5][6][8]
Wall condition and driving rain
Check first: damp, salts, exposure
Xella's brochure requires that the existing wall is protected from rising and penetrating moisture, with suitable driving-rain protection and working damp-proofing, and says rising damp and leaking facades generally rule out internal insulation.[4] The Redstone data sheets say construction defects and penetrating moisture must be remedied before boards are fitted.[6] Both ETA families apply only if the boards are protected from precipitation and wetting when built in.[1][5] The Finken study, as summarised in its abstract, is consistent with this; the Freimanis abstract adds that moisture behaviour differed greatly between brick types and that applying the adhesive tended to reduce rain-related moisture spikes.[13][12] The documents we read give no conservation-body guidance on calcium silicate boards specifically.
Thickness and thermal resistance
Trade-off: thickness against moisture function
Xella's brochure says experience shows capillary transport works regardless of wall build-up up to a maximum Multipor thickness of 100 mm, and that thicker boards or damp structures need a separate calculation.[4] Our arithmetic, using each maker's rated λ from the data sheets, thickness divided by λ: Multipor M4 at 100 mm gives R = 0.100 / 0.042 = 2.38 m²K/W; Redboard pro at its maximum assessed 120 mm gives 0.120 / 0.062 = 1.94; Redboard basic at 120 mm gives 0.120 / 0.080 = 1.50. For R = 1.0 the thicknesses are 42, 62 and 80 mm. Design values are set under national rules, and the boards are not directly interchangeable.[2][6][7][5] The documents we read give no comparison of calcium silicate with wood-fibre or cork internal insulation under the same conditions, so we draw none.
Rooms, finishes and substrates
Not suited without further measures
Xella says a vapour-open internal insulation cannot be used without further measures in rooms with high humidity such as spa areas and commercial kitchens, advises against tiling whole insulated external walls, and lists lightweight constructions as an unsuitable substrate. It names wallpapers, drywall boards and tiles as finishes that impair moisture transport.[4] Calsitherm gives the same warning about wallpaper.[10] Xella also advises keeping electrical installations to a minimum to avoid thermal bridges and using purpose-made insulated boxes.[4]
Handling, external use and what we did not read
Practical notes
Xella's EPD names band saws or hand-held carbide saws or cutters, Calsitherm's notes a handsaw, jigsaw or hand-held circular saw, and Calsitherm asks for dust protection when cutting indoors; we did not open a safety data sheet, so we make no statement on dust limits.[3][10] The Multipor ETA lists external wall insulation as an intended use but says use in thermal insulation systems such as ETICS needs separate ETAs, which we did not read; the Redstone ETAs cover internal use only.[1][5][8] We make no cost comparison and the documents we read give none.
Suppliers whose documents we read
Manufacturers whose ETAs, EPDs or data sheets we opened.
| Supplier | Products | Country | Documents seen |
|---|---|---|---|
| Xella (Xella Baustoffe GmbH; the data sheet names Xella Germany GmbH) | Multipor insulation boards M0 to M4 light, TIPwall and other system boards | Germany (Duisburg) | ETA-05/0093, 30 October 2024.[1] EPD-XEL-20250256-IBA1-EN, IBU, valid to 10/04/2030, listed on the IBU published list (checked 19 Oct 2026).[3] Data sheet, status 04/2022, hosted by a UK distributor.[2] Brochure edition 06/2025 (Xella Austria).[4] |
| Calsitherm Silikatbaustoffe (maker) and redstone (ETA holder, redstone GmbH & Co. KG) | Clima Redboard basic and pro, Clima Solid; Calsitherm Klimaplatte | Germany (Paderborn plant; Bremen) | ETA-19/0559 and ETA-24/1060.[5][8] Data sheets for Redboard pro and basic.[6][7] EPD-CAL-20240411-IBC3, IBU, valid to 21.11.2029, listed on the IBU published list (checked 19 Oct 2026); German version read.[9] Technical notes 2018.[10] |
| einzA (einzA Farben GmbH & Co KG) | Schimmelschutz Systemplatte (the April 2025 ETA named Calsitherm's plant; the current version names "Werk 3") | Germany (Hannover) | ETA-25/0390, 17 September 2025 (replaces the version of 24 April 2025), only.[11] |
Documents are summarised from manufacturer files, DIBt and the IBU list; confirm on the registry before specifying. We found no other maker whose documents we could open. Listing policy: editorial selection, not paid.
Frequently asked questions about calcium silicate insulation
What is Multipor, and is it calcium silicate insulation?
Multipor is Xella's mineral insulation board. Xella's data sheet describes it as made of calcium silicate hydrates from lime, sand, cement, water and a pore-forming agent, and its EPD names aluminium as the pore former. The EPD also calls it an autoclaved aerated concrete-based board.
What thermal conductivity do calcium silicate insulation boards declare?
In the European Technical Assessments we read, Xella's Multipor boards declare λD(23/50) of 0.040 to 0.047 W/(m·K) depending on grade, and Redstone's calcium silicate and cellulose boards declare 0.059 (Redboard pro) and 0.075 (Redboard basic, Clima Solid). The boards differ in density and composition.
Does calcium silicate insulation need a vapour barrier?
Xella's brochure describes its internal insulation as vapour-open and capillary-active and working without a vapour barrier, on walls protected from rising damp and driving rain; Calsitherm's technical notes describe its system as vapour-open and capillary-active. Xella says it cannot be used without further measures in rooms with high humidity such as spas and commercial kitchens.
What is the reaction to fire of calcium silicate insulation boards?
The ETAs we read give Euroclass A1 for Multipor and for the Redstone boards. The Redstone ETAs add that A1 is only proved if the boards are not additionally provided with paints, coatings or the like.
What carbon figures do the EPDs for calcium silicate insulation declare?
Xella's EPD declares GWP-total for A1 to A3 of 123 kg CO2e per m³ of board at 102 kg/m³. Calsitherm's EPD declares about 1,400 kg CO2e per tonne as an average across its boards at 259 kg/m³. The declared units and scopes differ, so the figures are not directly comparable.
The bottom line on calcium silicate insulation
Calcium silicate insulation is a family of boards with different densities, conductivities and strengths, so the ETA for the exact grade and the maker's system instructions are the documents that matter. The sources we read agree that the internal-insulation case depends on a dry, rain-protected wall and on keeping vapour-tight finishes off the boards; they do not settle how it compares with other internal insulations.
Related materials
Sources
- Deutsches Institut für Bautechnik (DIBt), European Technical Assessment ETA-05/0093, 30 October 2024 (English translation), Multipor insulation boards M0, M2, M3, M4 and M4 light, manufacturer Xella Baustoffe GmbH. Public technical assessment body; full PDF read. The DIBt download page (read 19 Oct 2026) lists this version without an expiry date. Used for declared λD, µ, density, strength, water absorption, intended uses and the ETICS limit. PDF · DIBt page
- Xella Germany GmbH, "Technical data sheet: Multipor mineral insulation systems, Multipor insulation board", status 04/2022, copy hosted by Back to Earth (UK distributor). Manufacturer data sheet, older than the 2024 ETA. Used for rated λ, ingredients, porosity, specific heat capacity, sorption moisture and listed certificates (we did not open those registers). PDF
- Xella Baustoffe GmbH, Environmental Product Declaration "Multipor mineral insulation board", EPD-XEL-20250256-IBA1-EN, Institut Bauen und Umwelt e.V. (IBU), EN 15804+A2, issued 11/04/2025, valid to 10/04/2030, independent verifier Matthias Klingler; declared unit 1 m³ at 102 kg/m³; the IBU published EPD list's data show the English and German versions with issue date 11 Apr 2025 and validity to 10 Apr 2030 (checked 19 Oct 2026). Manufacturer-commissioned. Full PDF read. EPD (PDF, hosted by Sto) · IBU list
- Xella Porenbeton Österreich GmbH, "Multipor Mineraldämmplatten: Einfach mineralisch dämmen und sanieren" (German), brochure edition 06/2025; the detail drawings are dated January 2023. Manufacturer brochure. Used for system build-up, substrate and moisture requirements, limits, the 100 mm guidance and finishes. PDF
- DIBt, European Technical Assessment ETA-19/0559, 30 October 2019, "Redboard basic" and "Redboard pro", holder redstone GmbH & Co. KG, manufacturing plant Calsitherm Silikatbaustoffe GmbH. Full PDF read; the DIBt page lists it without an expiry date. PDF
- redstone GmbH & Co. KG, "Technical Data Sheet Clima Redboard pro", status printed as 24/09/2026, copy hosted by Ecological Building Systems. Manufacturer data sheet. Used for rated λ, pH, water absorption coefficient, claims and installation. PDF
- redstone GmbH & Co. KG, "Technical Data Sheet Clima Redboard basic", status 12/12/2019 (hosted by Calsitherm). Manufacturer data sheet, older edition; on 19 Oct 2026 we found no newer Redboard basic data sheet on redstone's website, whose document links (hosted on a sign-in-only SharePoint) cover Redboard pro and Clima Solid. PDF
- DIBt, European Technical Assessment ETA-24/1060, 25 October 2024, "Clima Solid", holder redstone GmbH & Co. KG, manufacturing plant Calsitherm Silikatbaustoffe GmbH. Full PDF read. PDF
- CALSITHERM Silikatbaustoffe GmbH, Umwelt-Produktdeklaration "Mikroporöse Calciumsilikat-Wärmedämmstoffe", EPD-CAL-20240411-IBC3-DE, IBU, EN 15804+A2, issued 22.11.2024, valid to 21.11.2029, independent verifier Matthias Klingler; declared unit 1 t at 259 kg/m³; German version read in full; the IBU published list shows the German and English versions with validity to 21 Nov 2029 (checked 19 Oct 2026). Manufacturer-commissioned. EPD (PDF)
- Calsitherm, "Technische Hinweise" (German), 2018 edition. Manufacturer technical notes, older than the current ETAs. Used for the advice on wallpaper, dust protection and rising damp. PDF
- DIBt, European Technical Assessment ETA-25/0390, "einzA Schimmelschutz Systemplatte", holder einzA Farben GmbH & Co KG: version of 17 September 2025 (manufacturing plant "Werk 3"), which replaces the version of 24 April 2025 (manufacturing plant Calsitherm Silikatbaustoffe GmbH). Both full PDFs read; the DIBt page lists both (checked 19 Oct 2026). Used only for the plant, λD, density and strength statement. PDF, September 2025 · PDF, April 2025
- Freimanis, R., Blumberga, A., Vanaga, R. & Zundāns, Z. (2023). "Evaluation of the Impact of Bricks of Various Characteristics on Internally Insulated Masonry Walls in Cold Climate." Buildings 13(10):2529. Bibliographic data and abstract checked on Crossref; full text not accessed. Simulation study. doi:10.3390/buildings13102529
- Finken, G.R., Bjarløv, S.P. & Peuhkuri, R.H. (2016). "Effect of façade impregnation on feasibility of capillary active thermal internal insulation for a historic dormitory – A hygrothermal simulation study." Construction and Building Materials 113:202–214. Bibliographic data checked on Crossref (no abstract there); a summary of the abstract was read on the Aalborg University research portal, full text not accessed. Simulation study of several capillary-active materials. doi:10.1016/j.conbuildmat.2016.03.019