Molded vs pultruded grating comes down to how the glass fibers are arranged. Molded grating is cast in an open mold with a bidirectional fiber mat, so it carries load in both directions and tolerates field cutting. Pultruded grating is pulled through a heated die as continuous unidirectional roving, so it is far stronger along the bearing bars and spans longer distances with less deflection. Pick molded for complex layouts and cutouts; pick pultruded for long spans and heavy loads.
Both resist the corrosion that eats steel grating in chemical plants, marinas, and wastewater plants. But they are not interchangeable, and buying the wrong one costs you in material or in service life.
How Each Type Is Made
Molded grating is produced in an open cavity mold, a grid of square or rectangular pockets. Layers of glass fiber and catalyzed resin are built up in the mold until the panel is cured and ejected — a one-piece panel, commonly 3 ft x 10 ft or 4 ft x 12 ft, with a fixed mesh pattern.
Pultruded grating comes off a pultrusion line: continuous glass roving and mat are pulled through a resin bath, then through a heated steel die that shapes and cures the profile in one pass. Bearing bars emerge as I-bars or T-bars, and cross rods mechanically lock them into panels. Panel length is limited mainly by handling, not by a mold.
Fiber Architecture: The Real Difference
This is where the engineering decision lives.
Molded grating uses a bidirectional glass mat. Fibers run in both directions of the mesh, with glass content typically around 30 to 35 percent by weight. Load capacity is similar in both directions, which makes the panel forgiving: rotate it, cut it, and support it on any two edges.
Pultruded bearing bars are built from continuous unidirectional roving, often 60 to 65 percent glass by weight, wrapped in a surface veil. Nearly all the fiber runs along the bar, giving high strength and stiffness in the span direction — but the cross direction depends entirely on the tie rods.
Practical consequence: a molded panel behaves like a plate, a pultruded panel behaves like a set of beams. Design and installation have to respect that.
Load Direction, Span, and Deflection
For short spans — under about 2 ft with moderate loads — molded grating is usually sufficient and often cheaper per panel. It is the default for trench covers, small platforms, and pedestrian areas.
Once spans stretch past 3 ft, or loads get serious (forklifts, carts, equipment skids), pultruded grating pulls ahead. Its high fiber content delivers lower deflection at a given load, and deflection is usually the governing criterion for grating, not ultimate strength. Most engineers design FRP grating to a deflection limit of L/100 to L/240 — territory where pultruded panels comply and molded panels feel bouncy.
One caution: pultruded panels must be supported so the bearing bars span the open distance. Supporting the wrong edges wastes the panel’s strength. Our pultruded grating range covers multiple bar depths and spacings matched to typical span tables.
Resin Systems Apply to Both
Resin choice is mostly independent of process. Both types are commonly offered in:
- Isophthalic polyester — general industrial duty, good corrosion resistance, lowest cost.
- Vinyl ester — aggressive chemical environments: acids, caustics, bleaching agents, and wastewater headworks.
- Phenolic — where fire performance and low smoke are mandated, such as offshore platforms and tunnels.
Pultrusion adds one nuance: the resin must cure fast enough for a continuous line, so formulations are tightly controlled — every bar gets the same cure and the same properties. Match the resin to your chemical exposure first, then decide molded or pultruded on mechanical grounds.
Field Cutting and Installation
Molded grating is the friendlier panel on site. Its fibers run in both directions, so you can cut openings for pipes, columns, or hatches with standard carbide tools, and the panel keeps most of its integrity. Edges should be sealed to block wicking, but the panel still carries load around the cutout.
Cut a pultruded panel across its bearing bars and you have removed the structure. Penetrations must run parallel to the bars, or the opening has to be framed. Many buyers order pultruded panels pre-cut to drawing.
Cost Structure: Where the Money Goes
Neither type is universally cheaper. Molded grating concentrates cost in resin and in the mold itself, which is why non-standard mesh sizes carry premiums. Pultruded grating concentrates cost in glass fiber and in the precision dies that form the bars, which is why established die sets for common profiles offer the best value.
At the project level, pultruded panels often win on installed cost for long spans: fewer support beams and fewer joints. For a fuller breakdown, see the FRP grating price guide.
Comparison Table
| Factor | Molded FRP Grating | Pultruded FRP Grating |
|---|---|---|
| Process | Open-mold casting, panel by panel | Continuous pull through heated die |
| Fiber architecture | Bidirectional mat, ~30–35% glass | Unidirectional roving, ~60–65% glass |
| Load behavior | Two-way, plate-like | One-way along bearing bars, beam-like |
| Best spans | Short, up to ~2 ft typical | Long, 3 ft and beyond |
| Deflection | Higher at a given load | Lower; suits strict L/ limits |
| Field cutting | Cut anywhere; cutouts easy | Cut parallel to bars only; frame penetrations |
| Panel format | Fixed molded sizes (e.g., 3×10, 4×12 ft) | Bar spacing and length configurable |
| Cost driver | Resin content, mold tooling | Glass content, die sets; fewer supports |
| Typical uses | Trench covers, walkways, cutout-heavy platforms | Long-span walkways, vehicle loads, cooling towers |
Which One Should You Choose?
Choose molded when the layout is irregular, cutouts are numerous, spans are short, or loads are two-directional — trench covers, mezzanine cutouts, and retrofits where support locations are fixed.
Choose pultruded when spans are long, deflection limits are tight, loads travel in a known direction, or vehicle traffic is involved — conveyor walkways, offshore decks, cooling towers, and heavy industrial platforms.
If you are still weighing FRP against steel or aluminum, the fiberglass grating buying guide walks through the full selection logic.
FAQ
Is pultruded grating stronger than molded grating?
Along the bearing bars, yes. Pultruded bars carry roughly twice the glass content in a unidirectional layout, giving higher strength and stiffness in the span direction. Molded grating is stronger only in the cross direction.
Can molded and pultruded grating be used in the same facility?
Yes, and they often are. A common pattern is molded grating for trench covers and pultruded for long walkways. Keep support details and clip types consistent where the two systems meet.
Which resin should I specify?
Isophthalic polyester covers most general industrial exposure at the lowest cost. Choose vinyl ester for strong acids, caustics, or wastewater. Phenolic is for projects with strict fire and smoke requirements.
Can pultruded grating be cut on site?
Yes, but only parallel to the bearing bars or across a planned, framed opening. Cutting across load-bearing bars destroys the panel’s capacity. For complex penetrations, pre-cut panels are usually safer.
How do I know what span my grating can handle?
Work from the manufacturer’s published load tables, which list uniform and concentrated loads against span and deflection. Check deflection first — most FRP grating designs are governed by stiffness, not ultimate strength.
Is FRP grating slip resistant?
Both types are available with a gritted top surface for excellent slip resistance in wet and oily conditions. Meniscus surfaces are common on molded panels; pultruded panels typically use applied grit.
Get the Right Grating for Your Span and Load
IncomePultrusion is an FRP pultrusion manufacturer in Nanjing, China, supplying pultruded grating, structural profiles, rebar, fasteners, and pultrusion machinery with custom dies and OEM support — factory-direct. Send your span, load, and chemical exposure details and we will recommend bar depth, spacing, and resin. Contact us for a quote.
