The direct answer
SPC (Stone Plastic Composite) flooring core is composed of approximately 75% calcium carbonate (limestone) and 25% PVC — a 3:1 ratio by weight. This mineral-polymer composite gives SPC its core density of 1.95–2.05 g/cm³ and dimensional stability of ≤0.10% (EN ISO 23999). The calcium carbonate provides rigidity and mass; the PVC provides flexibility and click-joint integrity. Together, the 3:1 ratio is why SPC flooring remains flat across temperature changes that cause standard vinyl to lift at joints.
Why the Ratio Matters: Calcium vs PVC in the SPC Core
The name “Stone Plastic Composite” describes the compound directly — stone (calcium carbonate) and plastic (PVC). But the ratio between these two components is what determines whether the resulting core performs at commercial standard or fails in service. Specifically, it is the ratio — not the total thickness — that determines dimensional stability.
75%
Calcium Carbonate (CaCO₃) · Limestone
Provides mass, rigidity, and dimensional stability. The mineral component that gives SPC its stone-like resistance to point load deformation and thermal expansion. Core density: 1.95–2.05 g/cm³.
25%
PVC Polymer
Provides flexibility, impact absorption, and click-joint integrity. Without PVC, the core would be rigid stone — brittle and crack-prone under thermal cycling.
At the 3:1 ratio, the limestone provides enough mineral mass to achieve ≤0.10% dimensional stability — holding the floor flat across the temperature range of residential and commercial environments. Meanwhile, the 25% PVC provides enough polymer flexibility to prevent the core from becoming brittle under the repeated thermal cycling that every installed floor experiences.
The Complete SPC Plank Structure: Five Layers
The 3:1 calcium-to-PVC core is layer four of a five-layer construction. Each layer serves a distinct engineering function:
①
UV Coating
UV-cured topcoat. Scratch resistance (EN 16094 MSR-B2), chemical resistance Grade 5, and UV-yellowing protection across the product lifetime.
0.01–0.02mm
②
Wear Layer (Transparent PVC Film)
Determines commercial utilisation class. 0.3mm (Class 31/33) for residential and light commercial. 0.5mm (Class 33/42) for commercial. 0.7mm (Class 43/44) for heavy commercial. EN 660-2 Group T certified.
0.3–0.7mm
③
Décor Film (Photographic Print)
High-resolution print film. EIR process registers the print to the embossing die within ±0.1mm — the grain you see matches the grain you feel.
0.07mm · EIR ±0.1mm
④
SPC Rigid Core — The 3:1 Compound
75% calcium carbonate (CaCO₃) + 25% virgin PVC. Density 1.95–2.05 g/cm³. Dimensional stability ≤0.10% (EN ISO 23999). 100% waterproof. The engineering layer that determines the floor’s dimensional performance throughout its lifetime.
4–7mm · 1.95–2.05 g/cm³
⑤
IXPE Pre-attached Underlay
Cross-linked polyethylene foam. Pre-laminated — no separate underlay purchase required. Impact sound reduction △IIC 21 dB (ASTM E2179). Cushions minor subfloor irregularities under foot.
1mm · pre-attached
The Core Density: What 1.95–2.05 g/cm³ Means in Practice
The 3:1 calcium-to-PVC ratio produces a core density of 1.95–2.05 g/cm³. This is the correct technical expression of SPC core quality — not percentage ratios alone. Specifically, density is the parameter that procurement engineers can verify independently through third-party testing, whereas ratio claims cannot be easily verified without lab analysis.
| Parameter | Value | Standard & Context |
|---|
| Core Compound | CaCO₃ + Virgin PVC | 75% limestone + 25% PVC by weight. Virgin PVC only — no recycled content in Ecoflors SPC core. |
| Core Density | 1.95–2.05 g/cm³ | The verifiable expression of the 3:1 ratio. Third-party testable under ISO 1183. Consistently achieved across all Ecoflors SPC thicknesses. |
| Dimensional Stability | ≤ 0.10% | EN ISO 23999 · ASTM F2199. Across a 1,000mm plank, maximum dimensional change is 1mm. This is why expansion gaps remain necessary regardless of floor area. |
| Water Absorption | 0% · 100% waterproof | The limestone-PVC composite does not absorb moisture — neither the core nor the wear layer. Suitable for bathrooms, kitchens, and below-grade installation. |
| Hardness | Shore D 80–85 | The mineral density gives SPC significantly higher surface hardness than WPC or standard flexible PVC, contributing to residual indentation resistance. |
| Thermal Resistance | Low · UFH compatible | High mineral content conducts heat efficiently from underfloor heating systems. Maximum recommended UFH surface temperature: 27°C for residential systems. |
| Total VOC | TVOC ≤ 0.22 mg/m³ | GREENGUARD Gold (UL 2818). The PVC compound does not off-gas formaldehyde — SPC has no wood-based core that requires formaldehyde binders. |
What Happens When the Ratio Is Wrong
The 3:1 ratio is a balance point. Moving in either direction degrades performance in predictable ways:
Too much calcium · Above 4:1 ratio
Brittle Core · Thermal Cracking Risk
A calcium ratio above 4:1 (over 80% limestone) produces a core with insufficient polymer flexibility. The result is a plank that performs adequately at constant temperature but becomes brittle under the thermal cycling of real installation environments — particularly in climates with significant seasonal or diurnal temperature swings. Specifically, click-joint edges crack and the core can fracture at cut ends under repeated expansion and contraction cycles. Furthermore, higher calcium content also reduces impact resistance, making the floor more susceptible to cracking under point loads.
Too much PVC · Below 2.5:1 ratio
Soft Core · Reduced Stability
A calcium ratio below 2.5:1 (less than 70% limestone) produces a core with lower density and higher thermal expansion. The floor becomes softer underfoot, shows higher residual indentation under sustained point loads, and loses the dimensional stability that separates SPC from standard flexible LVT. Consequently, the dimensional stability figure rises above ≤0.10%, and the floor begins to behave more like a traditional flexible vinyl than a rigid-core product — with all of the joint movement and buckling risks that entails.
The 3:1 standard — why Ecoflors specifies density, not just ratio
Core density of 1.95–2.05 g/cm³ is the independently verifiable result of the 3:1 ratio. Ratio claims cannot be easily verified by a buyer’s procurement team. Density can be tested to ISO 1183 by any accredited lab. Consequently, Ecoflors specifies core density as the primary parameter in all technical data sheets — it is the figure procurement engineers can audit, not a self-declared ratio.
SPC vs WPC: Why Composition Determines Application
WPC (Wood Plastic Composite) replaces a portion of the calcium carbonate with a foamed wood-based filler. The result is a lighter, softer, warmer-underfoot product — at the cost of dimensional stability and density. For procurement decisions, the choice between SPC and WPC is application-driven:
SPC · Stone Plastic Composite
Commercial, High-Traffic, Extreme Environments
Core density 1.95–2.05 g/cm³. Dimensional stability ≤0.10%. Suitable for: commercial offices, retail, hospitality, healthcare, kitchens, bathrooms, below-grade basements, and underfloor heating. The high mineral density provides the stability and durability that commercial environments require. Moreover, SPC is the correct specification for any environment where dimensional stability under temperature change is a procurement requirement.
WPC · Wood Plastic Composite
Residential · Comfort Priority
Lower density. Higher thermal expansion than SPC. Softer and warmer underfoot — better acoustic and tactile comfort in residential environments where heavy commercial loading and extreme temperature swings are not concerns. However, WPC is not the correct specification for commercial environments, underfloor heating systems where thermal cycling is severe, or any project requiring EN ISO 23999 dimensional stability certification.
A Note on the ≤0.10% Stability Figure
Clarification — commonly misquoted as ≤0.05%
Some SPC product pages quote dimensional stability as ≤0.05%. The correct certified figure for commercial SPC under EN ISO 23999 is ≤0.10%. Ecoflors SPC consistently achieves ≤0.10% across all thicknesses — this is the value stated on third-party test reports and CE Declarations of Performance. A figure of ≤0.05% is not a standard EN ISO 23999 reporting threshold and should be questioned if encountered in competitor product documentation.
To put ≤0.10% in context: across a 1,000mm plank length, this means a maximum dimensional change of 1mm. Furthermore, expansion gaps at perimeter walls and transitions are still required in all SPC installations — the ≤0.10% figure describes material behaviour, not an installation guideline. Large, uninterrupted floor areas still require expansion joints regardless of material quality.
Frequently Asked Questions
What is SPC flooring made of?
SPC flooring core is approximately 75% calcium carbonate (limestone) and 25% PVC — a 3:1 ratio by weight. The complete plank is a five-layer construction: UV coating, wear layer (0.3–0.7mm), décor film, SPC rigid core, and pre-attached IXPE underlay. The core density of 1.95–2.05 g/cm³ and dimensional stability of ≤0.10% (EN ISO 23999) are the key performance parameters that result from this composition.
What is the ideal calcium-to-PVC ratio for SPC flooring?
The engineering standard is a 3:1 ratio — approximately 75% calcium carbonate to 25% PVC. This balance provides mineral rigidity (dimensional stability ≤0.10%) and polymer flexibility (impact resistance and click-joint integrity). A higher calcium ratio above 4:1 produces a brittle core prone to cracking under thermal cycling. A lower ratio below 2.5:1 reduces density and stability below the commercial performance threshold.
Does SPC flooring expand with temperature?
All materials expand with temperature change. SPC with a 3:1 calcium-to-PVC ratio achieves dimensional stability of ≤0.10% per EN ISO 23999 — meaning across a 1,000mm plank length, maximum expansion is approximately 1mm. Expansion gaps at perimeter walls and transitions are still required in all SPC installations. The ≤0.10% figure means SPC expands significantly less than standard flexible vinyl, not that it does not expand at all.
Is SPC flooring suitable for underfloor heating?
Yes. The dense limestone-PVC composite has low thermal resistance and conducts heat efficiently from UFH systems. The ≤0.10% dimensional stability ensures the floor remains flat and joint-tight across the UFH temperature cycling range — typically 18–28°C surface temperature for residential systems, and up to 27°C maximum surface temperature as the standard specification limit for SPC over UFH.
How does core density relate to the calcium-to-PVC ratio?
Core density is the independently verifiable result of the calcium-to-PVC ratio. The 3:1 ratio produces a density of 1.95–2.05 g/cm³, testable to ISO 1183 by any accredited laboratory. Ratio claims alone cannot easily be verified by a procurement team — density is the auditable parameter. Consequently, Ecoflors specifies core density on all technical data sheets as the primary compound quality indicator.
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