Reading the range
Every FilmTec element balances the same trade-off: tighter membranes reject more salt but need more pressure; looser ones save energy but pass more salt. The family prefixes tell you where each sits. (Figures below come from DuPont's standard test conditions, and those conditions are not the same across the range — 2 000 mg/L NaCl for the mainstream brackish elements, but 500 mg/L for the extra-low-energy ones such as XLE, and 32 000 mg/L for seawater. Rejection percentages are therefore not directly comparable family to family; they describe relative positioning. DWT holds the current datasheet for every element listed here, so confirm the exact numbers — and the conditions they were measured at — per element.)
The brackish workhorses
BW30 is the reference brackish element: stabilised salt rejection around 99.5% at standard test pressure, the default for feeds up to roughly 8 000 mg/L where permeate quality matters. Its sub-variants push particular corners: BW30HR / XHR for maximum rejection duty, BW30 PRO as the updated-performance generation, and fouling-resistant XFRLE builds for harder-working feeds.
LE (low energy) and XLE (extra low energy) trade a fraction of rejection (≈ 99.0 – 99.3%) for materially lower operating pressure — XLE runs standard tests at less than half BW30's pressure. They are the right answer where feed TDS is modest, energy or pump budget is tight, or a small system must perform on limited pressure. The cost is a slightly saltier permeate — usually irrelevant on low-TDS feeds, decisive on high ones.
ECO (PRO / PLATINUM) is DuPont's have-both family: high rejection (up to ≈ 99.7%) at low-energy pressures, the modern pick for municipal and industrial plants optimising lifetime energy cost.
The seawater family
SW30 elements are built for ~32 000 mg/L feeds at 55 – 83 bar. Within the family: SW30HRLE (high rejection, lower energy — the common industrial choice), SW30XLE / ULE (progressively lower energy), SW30XHR (maximum rejection), and fouling-resistant XFR. SEAMAXX sits at the lowest-energy end of seawater duty. Seawater elements on brackish feeds and vice versa are both mistakes: the SW membrane wastes pressure on the wrong duty, and a BW element at seawater pressures is outside its mechanical design.
The specialists
Fortilife (CR, XC, NF1000 variants) is the difficult-water family — designed for high-fouling wastewater reuse and minimal-liquid-discharge duty where standard elements foul or scale out. NF90 / NF270 / NF245 nanofiltration elements sit below RO on monovalent salt while still rejecting hardness, colour and organics at low pressure — softening-and-polishing without full desalination. The three are not interchangeable and the spread between them is wide: NF270 is the loose one that passes most of the sodium chloride, NF90 is tight enough to approach RO territory on salt, and NF245 falls between. Choose on the element datasheet and the salt you actually need to keep or pass, never on the family name. TW30 / BW60 (1812 format) are the residential point-of-use sizes, and AquaLast the extended-life 1812 option.
Choosing, in order
- Feed TDS picks the league: brackish families to ~8 000 mg/L; SW30 beyond, or where the brackish tail-end osmotic pressure climbs out of reach.
- Permeate spec vs energy picks the family: rejection-first (BW30HR/XHR), balanced (BW30, ECO), energy-first (LE/XLE).
- The water's behaviour adjusts it: fouling feeds toward FR/Fortilife builds; hardness-and-colour-only problems toward NF.
- Do not mix element types in one vessel on an ad-hoc basis — an unplanned mix leaves a flux imbalance that overworks the tighter elements, and the array performs to neither datasheet. The exception is a deliberate internally staged design, which DuPont publishes and supports: different elements in a defined order along the vessel, set by a projection rather than by what was on the shelf.
Rule of thumb: BW30 (or ECO) unless you have a reason; LE/XLE when the reason is pressure or energy; SW30 only for genuine seawater-class feeds; Fortilife and NF when the water itself is the problem. Then pull the actual datasheet — every element here is in DWT's spec-sheet library.