RO Flat Sheet Membrane Specifications
These RO flat sheet membrane specifications cover the material, types, rejection performance, and storage and handling of the thin-film composite membrane used to roll spiral-wound elements.
- TypeTFC polyamide
- Rejection99.0–99.7%
- GradesBW / SW / LE / FR
- SupplyWet, preserved
Key Takeaways
- The membrane is a thin-film composite (TFC) — polyamide on a support web.
- Choose the grade (BW / SW / LE / FR) for your feed water and pressure.
- Rejection and flux are a trade-off — balance them to the application.
- It ships wet and preserved; storage and handling protect performance.
The Membrane Is the Element’s Engine
RO flat sheet membrane is a thin-film composite: an ultra-thin aromatic polyamide rejection layer cast on a microporous polysulfone support, on a polyester backing web. The polyamide layer does the separation; everything else carries and supports it. It is the single most important — and most expensive — material in a spiral-wound element.
Get the grade and handling right and the finished element hits its rejection and flow targets. Estimate how much you need with the sheet usage calculator, and see how it fits the full build in the raw material selection guide.
RO Flat Sheet Membrane Specifications
Typical specifications for RO flat sheet membrane. Exact values depend on grade and are confirmed per order.
| Property | Typical specification |
|---|---|
| Construction | Thin-film composite (TFC): polyamide / polysulfone / polyester backing |
| Active layer | Aromatic polyamide |
| Grades | Brackish water (BW), seawater (SW), low / ultra-low pressure (LP / ULP, a.k.a. low energy), fouling resistant (FR) |
| Nominal salt rejection | 99.0–99.7% NaCl (grade-dependent) |
| Typical test conditions | Per grade (e.g. BW ~225 psi / 1500 ppm NaCl) — [confirm per grade] |
| pH tolerance (continuous) | ~2–11 (cleaning range wider) — [confirm per grade] |
| Free chlorine tolerance | < 0.1 ppm (polyamide is chlorine-sensitive) |
| Roll width | Cut to element leaf width (1812 to 8040) |
| Supply & storage | Wet, in preservative solution; cool, out of direct sun; keep from freezing |
| Shelf life | [Confirm per order] |
Choosing the Right Membrane Grade
The same construction is tuned into different grades. Match the grade to your feed water and energy target — rejection and flux always trade off.
Brackish Water
The general-purpose grade for industrial and commercial systems — high rejection at moderate pressure.
Seawater
Built for desalination: very high rejection at high feed pressure and salinity.
Low & Ultra-Low Pressure
Higher flux at lower feed pressure to cut energy cost (also called low-energy / LE), where feed water allows.
Fouling Resistant
Surface tuned to resist fouling on challenging or higher-turbidity feed water.
Match the Membrane Grade to Feed Water TDS
The fastest way to pick a grade is by the feed water your customer runs. Use the TDS bands below as a starting point, then confirm against the application.
| Feed water (TDS) | Membrane grade | Typical NaCl rejection | Typical application |
|---|---|---|---|
| < 1,000 ppm | LP / ULP (low / ultra-low pressure) | 98–99% | Tap-water polishing, low-energy systems |
| 1,000–10,000 ppm | BW (brackish water) | ~99.5% | Industrial & commercial RO |
| 10,000–45,000 ppm | SW (seawater) | ~99.7% | Seawater desalination |
| High fouling / wastewater | FR (fouling resistant) | ~99.5% | Wastewater reuse, high-turbidity feed |
Protect Performance Before It Is Rolled
Membrane performance can be lost before the element is even built. The polyamide layer must stay wet and clean: drying out, creasing, scratching or chlorine exposure all reduce rejection permanently. Keep rolls in their preservative packaging until use, and bring incoming material into your incoming inspection routine.
Because it is the highest-value material, membrane is where careful handling pays back most — and where defects are most expensive if missed.
Handle with care
- Keep wet — never let it dry out
- No creases, folds or scratches
- Avoid free chlorine contact
- Store cool, out of sun; don’t freeze
- Use within shelf life; FIFO stock
Membrane Problems Set the Ceiling on Every Element
No amount of good rolling fixes a compromised membrane. Its grade and condition cap what the finished element can do.
Wrong Grade
A mismatched grade misses the rejection or flux target for the application.
Damage in Handling
Drying, creases or scratches permanently lower rejection before rolling.
Chlorine Exposure
Even trace free chlorine degrades the polyamide layer irreversibly.
Need RO flat sheet membrane for production?
Send us your feed water analysis and element sizes — our engineers will recommend the right membrane grade free of charge, then supply it to spec.
Flat Sheet Membrane FAQ
What is RO flat sheet membrane made of?
It is a thin-film composite (TFC): an ultra-thin aromatic polyamide rejection layer on a microporous polysulfone support, on a polyester backing web. The polyamide layer performs the salt rejection.
What salt rejection does RO flat sheet membrane achieve?
Nominal NaCl rejection is typically 99.0–99.7%, depending on the grade and test conditions. Seawater grades sit at the high end; low-energy grades trade some rejection for higher flux.
Which membrane grade should I use?
Match the grade to your feed water and energy target: brackish water (BW) for general use, seawater (SW) for desalination, low energy (LE) to cut pressure and cost, and fouling resistant (FR) for challenging feed. Share your feed water for a recommendation.
How should RO membrane be stored?
Keep it wet in its preservative packaging, cool and out of direct sun, and do not let it freeze or dry out. Avoid creases, scratches and any free-chlorine contact, and use within its shelf life on a first-in, first-out basis.