| HS Code | 317568 |
| Product Name | HIUV S201W EVA White Encapsulant Film |
| Side Application | Rear Side |
| Grade | Optical Enhancement Grade |
| Material | Ethylene-Vinyl Acetate (EVA) with white diffusing agent |
| Color | White |
| Thickness | 0.50 mm |
| Density | 1.52 g/cm³ |
| Light Reflectance | ≥90% |
| Crosslinking Degree | ≥80% |
| Volume Resistivity | ≥1.0×10^15 Ω·cm |
| Water Vapor Transmission Rate | ≤20 g/(m²·day) |
| Tensile Strength | ≥35 MPa |
| Elongation At Break | ≥400% |
| Thermal Shrinkage | ≤3% (MD/TD, 150°C, 30min) |
| Peel Strength To Glass | ≥60 N/cm |
| Peel Strength To Backsheet | ≥40 N/cm |
As an accredited HIUV S201W EVA White Encapsulant Film,Rear Side,Optical Enhancement Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Each package contains one roll of HIUV S201W EVA White Encapsulant Film, rear side, optical enhancement grade. |
| Container Loading (20′ FCL) | 20′ FCL: palletized rolls of HIUV S201W EVA white encapsulant film, rear-side optical grade, securely packed for export. |
| Shipping | Shipping: Supplied in moisture-proof, sealed rolls with protective wrapping to prevent damage. Handle with care to avoid creasing or tearing. Store and transport upright in dry, ventilated containers, avoiding extreme heat or humidity. Standard export packaging ensures safe delivery of this optical-grade EVA film. |
| Storage | Store HIUV S201W EVA film in its original sealed packaging in a cool, dry, well-ventilated area. Avoid direct sunlight, moisture, and high temperatures; recommended storage below 30°C with humidity under 60% RH. Keep away from heat sources and chemicals. Use within the specified shelf life, typically within six months from receipt. |
| Shelf Life | Shelf life: 12 months from date of manufacture when stored in original packaging at cool, dry conditions below 30°C. |
On a 2.2 m × 4.4 m dual-chamber vacuum laminator running 182 mm half-cut PERC strings, S201W is positioned between the rear side of the interconnected cell matrix and a 0.30 mm PVDF/PET/PVF backsheet. The layup is 3.2 mm low-iron tempered front glass, 0.55 mm transparent EVA, cell strings with 2 mm inter-cell gaps, 0.45 mm S201W, and 0.30 mm backsheet. The replacement ratio is one-to-one against a clear rear EVA of equal thickness; the S201W layer contributes 0.44 kg/m² to 0.48 kg/m² depending on density. Cure is conducted at a platen setpoint of 145 °C to 150 °C for 8 to 12 min at 50 Pa chamber pressure and 0.10 MPa membrane pressure. The peroxide-initiated crosslinking reaction is monitored by ASTM D2765-16 Method A; gel content must exceed 80% for lamination release. Adhesion is tested per ASTM D1876 at 180° and 100 mm/min, with a typical acceptance threshold of 40 N/cm at the glass/EVA and EVA/backsheet interfaces. Reflectance of this white encapsulant class is measured according to ASTM E1331-15 with an integrating sphere; hemispherical reflectance above 90% across 400 nm to 1100 nm is achievable. The module-level optical gain is not a film-only property; it is coupled to cell spacing, string gap, backsheet reflectivity, and active area. Widening the inter-cell gap from 2 mm to 5 mm increases reflected photon collection but reduces active cell area, so the current-voltage trade-off is layout-specific. Lamination below 138 °C yields gel content below 70% and adhesion loss; upper platen temperature above 155 °C accelerates peroxide over-cure, bubble formation, and yellowness index shift above ΔYI 2 per ASTM E313. S201W is not compatible with bifacial rear-side irradiance because the white layer blocks rear transmission. The practical cure window is therefore within ±5 °C of 145 °C for standard backsheet constructions. Finished products are 72-cell and 78-cell monofacial modules with 182 mm or 210 mm wafers rated 550 Wp to 590 Wp. Qualification is performed under IEC 61215-1:2021 and IEC 61730-1:2023.
| Standard or method | Test condition | Purpose in S201W line |
|---|---|---|
| IEC 61215-1:2021 MQT 11 | Thermal cycling −40 °C to +85 °C | Module design qualification |
| IEC 61215-1:2021 MQT 13 | Wet leakage current under immersion | Insulation integrity after lamination |
| IEC 61730-1:2023 | Module safety construction and component requirements | Safety qualification |
| ASTM D2765-16 Method A | Solvent extraction of crosslinked EVA | Gel content verification |
| ASTM D1876 | 180° T-peel at 100 mm/min | Adhesion to glass and backsheet |
| ASTM E313 | D65/10° yellowness index | Optical aging and over-cure control |
Commercial rooftop lines running 108 half-cut 182 mm cells with polyamide-based fire-rated backsheets use S201W as the rear white reflector in a stack of 3.2 mm front glass, 0.50 mm transparent front EVA, cell strings, 0.45 mm S201W, and 0.35 mm fire-rated backsheet. The S201W mass fraction is approximately 7.5 wt% of a 20 kg module. In single-chamber laminators with heated platens, the platen setpoint is trimmed to 148 °C and total cure time is 10 to 12 min; upper membrane pressure is kept at 90 kPa because thicker fire-rated backsheets with lower thermal conductivity shift the rear interface temperature ramp. Cure must still produce gel content above 80% per ASTM D2765-16 Method A and peel adhesion above 40 N/cm per ASTM D1876. Fire-rated backsheet surface temperature is monitored by contact thermocouple and should remain below 140 °C while the EVA reaches cure threshold; the process window is therefore narrower than with standard PVF backsheets. If S201W roll stock has been exposed to ambient RH above 60%, the film is conditioned at 25 °C and ≤30% RH for 4 h before layup to reduce moisture-induced bubble defects. Qualification of the finished laminate is performed under UL 61730-1:2023 and IEC 61215-1:2021; system-level fire classification is tested per the applicable national building code, not on the encapsulant alone. Terminal products are 400 Wp to 450 Wp commercial rooftop modules with 108 half-cut cells. The white rear layer improves internal reflection in areas between cells, but the optical benefit is reduced when cell coverage is dense and the backsheet has low reflectance; published data for this specific fire-rated backsheet pairing is limited.
Double-glass monofacial spandrel and carport modules use S201W to create a diffuse reflective rear boundary without adding a separate white backsheet. The layup places S201W between the cell strings and a 2.0 mm semi-tempered rear glass: 3.2 mm heat-strengthened front glass, 0.56 mm transparent EVA, 182 mm half-cut cells, 0.45 mm S201W, and 2.0 mm rear glass. The S201W addition corresponds to 0.44 kg/m² and about 7.0 wt% to 8.0 wt% of a 22 kg glass-glass module. Lamination is performed at 150 °C for 14 to 18 min with vacuum ramp from 100 Pa to 50 Pa before 0.10 MPa membrane pressure is applied; the second glass pane increases thermal mass and delays the heat ramp at the rear EVA interface, so cure time is longer than in backsheet builds. Gel content is checked by ASTM D2765-16 Method A and must exceed 75% because rigid glass-glass packages impose higher interfacial shear during thermal cycling. The interface between S201W and rear glass is tested by ASTM D1876 peel; initial adhesion is typically above 40 N/cm. The S201W white rear layer is limited to monofacial glass-glass constructions; it blocks rear-side irradiance and therefore cannot be used where bifacial gain is required. Moisture control is critical: glass is dry, EVA is stored at ≤30 °C and ≤60% RH, and roll stock exposed above 60% RH is conditioned at 25 °C and ≤30% RH for 4 h before layup. Qualification is performed under IEC 61215-1:2021 and IEC 61730-1:2023; where building codes require reaction to fire, the finished module is tested under EN 13501-1:2018 or equivalent. Terminal products are custom-sized glass-glass monofacial BIPV spandrel panels, carport roof modules, and greenhouse roof modules rated 150 Wp to 350 Wp depending on area.
Shingled-cell module architectures use S201W behind overlapping cell strings to maintain rear optical confinement while filling the non-planar topography created by shingled interconnects. The rear encapsulation layup places S201W between the rear side of shingled strings and a PVF/PET/PVF backsheet or rear glass. The nominal S201W thickness is 0.45 mm; front transparent EVA is 0.55 mm, and the rear film mass per active area is approximately 0.44 kg/m². Lamination is performed at 145 °C platen setpoint for 10 to 12 min with membrane pressure reduced to 0.08 MPa to 0.09 MPa; the lower pressure reduces shear stress on conductive adhesive joints during melt flow. Crosslinking is confirmed by ASTM D2765-16 Method A with gel content above 75%. The melt flow index of this EVA class is typically 12 to 25 g/10 min at 190 °C/2.16 kg per ISO 1133-1:2022, which allows gap filling between shingled cell edges. Adhesion is evaluated by ASTM D1876; peel values above 40 N/cm are typical after lamination, but shingled-joint shear is monitored separately on finished modules. The process window is constrained: below 140 °C gel content falls below the release threshold, and above 152 °C the conductive adhesive may degrade and the rear encapsulant may yellow beyond ΔYI 2 per ASTM E313. Thickness uniformity after lamination is checked by cross-sectional microscopy because the rear encapsulant must compensate for cell-to-cell shingle overlap. S201W is not used in bifacial shingled modules; rear-side irradiance is blocked by the white layer. Terminal products are high-density residential and commercial modules rated 400 Wp to 450 Wp with shingled 182 mm cells. Qualification of finished modules is performed under IEC 61215-1:2021 and IEC 61730-1:2023; published data for this specific shingled configuration is limited.
Flexible off-grid modules below 100 Wp produced on compact flat platen laminators use S201W at reduced thickness to maintain rear reflectivity under bending and field transport conditions. The layup consists of a fluoropolymer composite front sheet, 0.30 mm transparent EVA, 156 mm or 158.75 mm monocrystalline cell strings, 0.30 mm S201W, and a polymer rear sheet. The S201W film at 0.30 mm nominal thickness supplies approximately 0.29 kg/m² to 0.32 kg/m²; it is not blended into a liquid formulation but is placed as a pre-cast film. Lamination is conducted at 135 °C to 140 °C for 10 to 12 min under 50 Pa vacuum and 0.06 MPa to 0.08 MPa membrane pressure; the lower pressure reduces cell displacement and edge squeeze-out in flexible builds. Gel content is verified by ASTM D2765-16 Method A above 70%, and peel adhesion is tested per ASTM D1876 at 100 mm/min. The white rear encapsulant returns light that passes between cells to the rear surface; in dense single-cell laminates with minimal string gaps, the optical gain is smaller than in multi-cell modules with wider spacing. S201W should not be used where the rear side must remain transparent or where continuous bending radius below 300 mm creates interfacial shear beyond the adhesion limit; published data for this specific flexible configuration is limited. Industry compliance is established under IEC 61215-1:2021 for framed designs and IEC 61730-1:2023 for safety; flexible builds without a rigid frame additionally require customer-specific bending, scratch, and humidity cycle tests. Terminal products are 50 Wp to 100 Wp portable solar chargers, off-grid water pump panels, and mobile power components.
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HIUV S201W is an ethylene-vinyl acetate (EVA) white encapsulant film formulated for rear-side lamination in monofacial crystalline silicon photovoltaic modules. The optical enhancement grade designation reflects the use of a controlled dispersion of inorganic white pigment in a peroxide-curable EVA matrix, together with silane adhesion promoters, antioxidants, and ultraviolet stabilizers. In the module layup, S201W is positioned between the cell string and the rear backsheet, where it increases rear-side diffuse reflectance and redirects light that would otherwise be lost through cell spacing or absorbed by a dark backsheet. That rear-side optical function distinguishes S201W from transparent EVA encapsulants, which are specified primarily for front-side broadband transmittance and low haze rather than backscatter. The film is supplied as an embossed roll, with surface texture intended to allow air evacuation during flat-bed vacuum lamination. Typical stock thicknesses for rear-side white EVA are 0.45 mm, 0.50 mm, and 0.55 mm; roll width and length are slitting- and packaging-dependent and must be read from the lot datasheet rather than assumed from generic EVA literature.
Optical enhancement in S201W does not arise from simple addition of white pigment. The pigment must be dispersed below the wavelength-scale agglomerate size to maximize diffuse scattering while maintaining dielectric strength. In masterbatch and film production, disperser speed, mill gap, and melt temperature influence pigment particle size; excessive shear can degrade EVA molecular weight and increase melt flow, while insufficient shear leaves agglomerates. Incoming reflectance maps across the roll can reveal streaking, and visual inspection under 2000 lux is used to reject gels, fish-eyes, and edge contamination. Dielectric weakness from carbon specks or pigment agglomerates is screened by wet leakage current and hipot tests after module lamination according to the qualification clauses of IEC 61215-2:2021.
For incoming material control, composite lot release is commonly checked for thickness profile by mechanical scanning according to ISO 4593:1993, density by ASTM D792-20, and pre-cure tensile behavior by ASTM D882-18. Published data for HIUV S201W lot-specific values may require manufacturer confirmation; typical EVA white encapsulant films in this class exhibit density in the range 0.95–1.05 g/cm³, tensile strength before cure of 4.0–8.0 MPa, and elongation at break of 300–500%. The melt flow rate of the pre-crosslinked compound, measured at 190 °C under 2.16 kg load according to ISO 1133-1:2022, is generally controlled between 20 g/10 min and 35 g/10 min. Batch-to-batch variation outside ±5 g/10 min is a process warning because it can alter edge bleed and cell gap filling on fixed lamination recipes.
White EVA rear-side film is not evaluated by front-side solar-weighted transmittance in the same way as a front-sheet encapsulant. The relevant optical response is hemispherical reflectance after lamination, because the final reflection depends on pigment concentration, backsheet color, glass interface, and cure-induced morphological changes. A typical incoming reflectance specification for white EVA rear-side film is 88–94% at 550 nm measured according to ASTM E1331-15; values below 85% usually indicate pigment dispersion problems, excessive dilution from low-quality recycle content, or lamination against a dark backsheet with insufficient film coverage. For module-level optical gain, reflectance alone is not sufficient. The increase in short-circuit current density should be verified with the same cell string spacing and backsheet as the production bill of materials, using the spectral response correction procedures of IEC 60904-7 or an integrating-sphere quantum efficiency measurement. Published data for HIUV S201W module-level current gain in a specific customer backsheet stack is limited; therefore, a dedicated lamination trial is required before assigning a gain target.
In lamination, the cure cycle must reach full crosslinking without overheating the polymer. A flat-bed laminator with silicone membrane and vacuum capability below 1 mbar absolute is standard for these films. A typical starting recipe for 0.45 mm S201W uses a vacuum stage of 240–360 s at 140–150 °C, followed by a press stage of 600–900 s at 0.8–1.0 bar. Cure is confirmed by gel content after lamination, specified at ≥75% by ASTM D2765-16. Incomplete cure leaves unreacted vinyl acetate groups and residual peroxide. During damp heat exposure, those residues can generate acetic acid, which promotes corrosion of solder ribbons and busbars, delamination at glass and backsheet interfaces, and yellowing. Therefore, lamination lines should not attempt to increase throughput by reducing cure time below the point at which the center of the thickest laminate cross-section reaches the specified gel content.
The processing window for white EVA is narrower than for unpigmented EVA because the filler increases melt viscosity and thermal mass. If lamination temperature exceeds 155 °C for an extended period, oxidative degradation can yellow the rear-side layer and reduce reflectance; if the laminate remains below 140 °C, peroxide decomposition is sluggish and the final gel content may remain below 70%. Platen temperature uniformity should be held within ±2 °C across the load, and hot spots should be mapped with a contact thermocouple array or equivalent thermal profiler. For half-cell or shingled strings, the higher filler content can produce greater cell-edge stress; press pressure should be reduced in 0.1 bar increments if cell cracking occurs in the first production run.
The film should be stored at ≤30 °C and ≤60% relative humidity in original packaging. Rolls conditioned below 20 °C should be acclimatized for 8–12 h at 20–25 °C before opening to prevent condensation. Once opened, rolls used in ambient relative humidity above 60% should be consumed within 72 h or sealed with desiccant. Adhesion loss and bubble formation in the lamination line are often traced to moisture in the backsheet or glass rather than the EVA roll alone; moisture-sensitive backsheet constructions may require pre-drying at 75–85 °C for 4–6 h before layup. Avoid direct contact with amine-containing cleaners or adhesion promoters not qualified for peroxide-curing EVA; such materials can interfere with the crosslinking system and produce premature gel or unstable bonding.
Transparent EVA on the rear side of a monofacial module does not create the same controlled backscatter. In a dark-backsheet module, rear-side light that passes through transparent EVA is largely absorbed by the backsheet and contributes little to cell current. S201W is therefore selected when the rear-side encapsulant layer must act as a scattering medium while the backsheet continues to provide electrical isolation and environmental protection. The optical gain is not equivalent to bifacial operation: S201W is unsuitable for bifacial modules in which rear-side transmission is required for rear-irradiance collection. For bifacial glass-glass construction, a transparent rear-side encapsulant or a POE-based system should be used unless the module design specifically blocks rear-side light.
Compared with polyolefin elastomer rear-side films, S201W retains the typical EVA advantages of higher adhesion to glass and polyester backsheets and lower material cost per unit area. However, EVA chemistry releases acetic acid under severe damp heat, especially when crosslinking is incomplete or when the module is stored at high humidity without adequate edge seal protection. Modules using corrosion-sensitive heterojunction cells or copper-based front metallization may require POE or co-extruded EVA-POE rear-side encapsulant to reduce acetic acid exposure. S201W also differs from generic white EVA by its optical enhancement classification, which implies tighter control of pigment particle size distribution and dispersion quality. Poor dispersion in white EVA can create visible streaks, local dielectric weak points, and reflectance variation across the module; those defects are not corrected by lamination and can trigger incoming inspection rejection.
Table 1 compares the classes of rear-side encapsulant under common rear-side service conditions. The values are class-typical and are not a substitute for the HIUV S201W certificate of analysis.
| Property | HIUV S201W white EVA | Transparent EVA | POE rear-side |
|---|---|---|---|
| Rear-side optical function | Diffuse reflectance | Transmissive | Transmissive or white grades |
| Typical post-lamination gel content | ≥75% by ASTM D2765-16 | ≥75% by ASTM D2765-16 | ≥70% by ASTM D2765-16 |
| Acetic acid release under damp heat | Yes, controlled by cure | Yes, controlled by cure | No acetic acid |
| Adhesion to glass | High | High | Moderate to high, requires silane or primer |
| Suitability for bifacial rear-side transmission | No | No | Yes, with transparent grade |
| Typical application position | Rear side, monofacial | Front or rear | Front or rear, high-voltage or sensitive cells |
On production lines, roll unwind tension should be maintained below 50 N/linear meter to prevent creasing. Cell spacing down to 2.0 mm can be used provided the melt flow and emboss pattern allow air evacuation; edge bleed and busbar impression should be monitored after the first production run. Shrinkage is controlled below 3.0% after 30 min at 150 °C by ASTM D1204-14. Shrinkage above this limit can produce edge pull-in, glass bow change, or backsheet wrinkling in modules longer than 2 m.
The following release and incoming inspection schedule is used to verify that rear-side white EVA meets the minimum module qualification and line control requirements. Each test should be performed on retained samples from the same roll slit or lamination trial as the production lot.
| Control item | Test method | Typical specification |
|---|---|---|
| Thickness profile | ISO 4593:1993 | Within ±0.03 mm of nominal |
| Density | ASTM D792-20 | 0.95–1.05 g/cm³ |
| Melt flow rate at 190 °C/2.16 kg | ISO 1133-1:2022 | 20–35 g/10 min |
| Tensile strength before cure | ASTM D882-18 | 4.0–8.0 MPa |
| Elongation at break before cure | ASTM D882-18 | 300–500% |
| Gel content after lamination | ASTM D2765-16 | ≥75% |
| Volume resistivity after lamination | ASTM D257-14 | ≥1.0 × 1014 Ω·cm |
| Hemispherical reflectance at 550 nm | ASTM E1331-15 | 88–94% |
| High-temperature shrinkage | ASTM D1204-14 | ≤3.0% |
Because rear-side white EVA reflectance is influenced by pigment concentration, cell gap, backsheet color, and lamination thermal history, incoming reflectance measured on free film is not sufficient to predict module-level current gain. A production trial should include the same glass, cell string, busbar, and backsheet stack as the final module, and the resulting laminate should be evaluated for gel content, adhesion, wet leakage current, and damp-heat visual change according to the applicable clauses of IEC 61215-2:2021. In addition, optical gain should be confirmed by short-circuit current or quantum efficiency comparison rather than by reflectance alone. Published data for HIUV S201W module-level gain in specific laminate stacks is limited; conversion efficiency claims therefore require dedicated run data.
Process deviations observed on production equipment include edge bleed due to high melt flow or excessive press pressure, bubble entrapment when vacuum time is shortened below the film emboss evacuation limit, and post-laminate delamination when glass or backsheet surface preparation leaves organic residues. S201W does not mask those upstream defects; its rear-side scattering function remains intact only when the encapsulant is fully cured and bonded without interfacial voids.
