A: At DEFI structural fiberglass, we use three methods of fiberglass, pultrusion, open-molded, and hand layup. Pultrusion is something you would typically see in a fiberglass channel, beam, or even square tube that we use in handrails and ladders.
Open molded typically refers to the fiberglass grating, open molded grating.
The hand layup is when we would use a hand layup mold to make a special product or shape.
If you found us searching for “fiberglass reinforced plastic,” you probably saw more terms than you expected. FRP, GRP, GFRP, structural fiberglass, pultruded profiles, it’s a lot of overlapping language for a handful of related materials.
The short version: FRP is the umbrella term for any plastic reinforced with fibers, and not all of those fibers are glass. In the US, “FRP” usually means structural fiberglass, what we build at DEFI.
When engineers ask for more rigid fiberglass profiles, they mean pultruded, thermoset composite profiles, the stiffest of the three fiberglass fabrication methods, used across construction and industrial applications.
Key Takeaways
Fiberglass is made by spinning molten glass into fiber strands, then combining it with resin to form FRP (fiber-reinforced polymer).
Rigid fiberglass profiles are thermoset FRP shapes, angles, channels, I-beams, tubes, made by pultrusion, the stiffest and strongest of the three fiberglass fabrication methods.
DEFI uses three fabrication methods: pultrusion (rigid structural profiles), open mold (grating), and hand layup (custom shapes).
Pultruded thermoset profiles have an elastic modulus of roughly 17-50 GPa and tensile strength of 207-690 MPa, well below steel’s 200 GPa modulus but far ahead on strength-to-weight
Vinyl ester resin pultruded profiles can hold corrosion rates below 0.001 mm/year and service lives past 30 years in chemical and offshore environments without a protective coating.
What Are Rigid Fiberglass Profiles?
More rigid fiberglass profiles, pultruded, thermoset composite profiles such as angles, channels, I-beams, tubes, and custom cross-sections, hold their form under load instead of flexing like a thermoplastic. They’re “rigid” because the resin that binds the glass fibers is a thermoset, not a thermoplastic.
That rigidity shows up in the numbers. Pultruded FRP typically runs an elastic modulus of 17-50 GPa. Composite profiles regularly beat the European EN 13706 E23 standard’s 23 GPa minimum, landing closer to 30 GPa with tensile strength near 500 MPa, about double the 240 MPa the standard requires. That stiffness, combined with a thermoset resin’s dimensional stability, is what lets a rigid fiberglass I-beam or channel carry a structural load the way a steel beam does, without the creep a thermoplastic part would show.
What Is Fiberglass?
Fiberglass is created by spinning melted glass so it forms fine fiber strands, almost like cotton candy in consistency. On its own, fiberglass can be a usable product, but it’s most valuable as the reinforcement inside a composite like FRP.
A composite combines a matrix (resin) with a reinforcement material. The matrix can be plastic, metal, or ceramic; in FRP, fiberglass is the reinforcement that makes the finished composite stronger than either material alone.
What Is FRP?
FRP stands for fiber-reinforced plastic (or polymer). A polymer is a chemical compound built from long, chain-like molecules, some natural, like rubber, some synthetic, like polypropylene. Pliable synthetic polymers such as polypropylene are thermoplastics; more rigid ones, cured into a permanent cross-linked structure, are thermosets. FRP is the raw material manipulated into the structural profiles we build, hence “structural fiberglass.”
What Is Structural Fiberglass?
Structural fiberglass is building components manufactured from standard fiberglass profiles, angles, tubes, I-beams, and other shapes. Most of our products are made using three fabrication methods, chosen by end use: pultrusion, open mold, and hand layup.
Method | What it makes | Rigidity | Typical use |
|---|---|---|---|
Pultrusion | Angles, channels, I-beams, tubes | Highest, continuous thermoset profile, no distortion | Handrails, ladders, structural beams, structural profiles |
Open mold | Grating panels | Rigid in-plane; shaped by mold | Walkways, platforms, trench covers |
Hand layup | Custom shapes, tanks, vessels | Depends on layup skill and fiber orientation | One-off parts, helmets, specialty covers |
Most of DEFI’s top-selling FRP products are fabricated by pultrusion. Due to the nature of that process, pultruded profiles carry several advantages over the other two methods: increased strength, higher corrosion resistance, and better impact resistance.
What Is Pultrusion?
Pultrusion is a continuous manufacturing process that creates rigid structural fiberglass shapes without distorting the cross-section, used across construction and industrial applications wherever a high-strength, corrosion-proof profile has to replace steel. Fiberglass reinforcement, continuous roving, filament mats, or strand mat, is pulled through a resin bath and then a heated die that cures the resin and sets the shape.
The resin cures through a catalytic reaction driven by the die’s heat, becoming a rigid thermoset that locks in the die’s cross-section. Pultrusion is used across industries precisely because it reproduces the strong properties of traditional materials like steel while correcting their weak points (corrosion, weight, conductivity). Pultruded structural fiberglass grating, for instance, duplicates the strength of steel grating but resists corrosion the way steel can’t. Variations exist, reciprocating pullers, caterpillar pullers, but the core concept, pulling fiber through a heated die, stays the same.
Hand Layup & Open Mold Process
Open molding is one of the oldest FRP processes and needs no complex machinery. It suits low-volume, labor-intensive, larger products such as tanks, vessels, and pipelines.
The mold dictates the final shape, so finish matters: a female mold produces a smooth exterior, a male mold a smooth interior, and any defect in the mold shows up in the finished part. Because the resin is poured in liquid, a release agent, wax, polyvinyl alcohol, or mylar film, keeps the cured part from bonding to the mold.
Hand layup is an open mold process done entirely by hand, so quality depends heavily on the technician’s skill. Safety helmets and custom shapes are typical hand layup products.
Resin Systems: Why the Matrix Determines Rigidity and Corrosion Resistance
Picking the resin is the single biggest factor in how a rigid fiberglass profile performs in service, not just the fiber. The three resins used in pultruded FRP trade off cost, chemical resistance, and mechanical performance.
Resin | Rigidity / strength | Chemical resistance | Typical use |
|---|---|---|---|
Polyester (iso/ortho) | Good, cost-effective | Moderate; not for concentrated acids | General construction, low-corrosion applications |
Vinyl ester | Good, 50-100% cost premium over polyester | Superior, acids, chlorides, offshore/marine | Chemical plants, wastewater, offshore |
Epoxy | Highest mechanical properties, up to 690 MPa tensile | Excellent, plus superior electrical resistivity (10¹²–10¹⁶ Ω·m) | Electrical infrastructure, high-performance structural members |
For DEFI’s petrochemical and offshore customers, vinyl ester is almost always the right call, the same resin logic covered in our petrochemical FRP applications guide.
60-70% is E-glass roving, continuous strand mat, and surfacing veil; the remaining 30-40% is the resin matrix plus additives like UV stabilizers and flame retardants.
The Advantages of Pultruded Structural Fiberglass
There’s a reason pultruded fiberglass is our top seller. The raw materials and the pultrusion process combine to give rigid structural FRP benefits steel can’t match:
Extreme corrosion resistance, less than 0.001 mm/year in vinyl ester
Superior strength-to-weight ratio, roughly ⅓ the weight of steel, and up to four times lighter in some applications
Non-slip attributes baked right into the surface
Non-conductive, safe around electrical equipment
Easy installation with basic hand tools
Extreme heat resistance for the resin system specified
In addition, there are inherent advantages no other material can duplicate.
Durability
Manufacturing plants with chemical corrosives or harsh outdoor exposure wear steel down fast, rust, flaking, and in neglected cases, structural failure. Rigid FRP profiles shrug off that same exposure with no structural damage. You never have to worry about a pultruded profile’s integrity being compromised by the environment it’s installed in.
Long-Term Value
Pultrusion produces the highest output volume at the lowest conversion cost of the three fabrication methods, and the profile itself needs no maintenance afterward. FRP is lighter and cheaper to ship than steel, and unlike steel, which often needs cranes and heavy rigging, it can be moved with a forklift or carried by hand.
Safety
Steel’s safety can be compromised by electrical hazards, corrosives, and weather. DEFI’s FRP handrails are built in designs that exceed OSHA requirements, and special resin combinations add heat and fire resistance to our vinyl ester and polyester handrails. We can also bake in any color, including safety yellow, with UV barrier coatings for long-term UV resistance.
Rigid Fiberglass Profiles vs. Steel: Quick Comparison
Property | Pultruded FRP (rigid) | Structural Steel (A36) |
|---|---|---|
Tensile strength | 207-690 MPa | 250-400 MPa |
Elastic modulus | 17-50 GPa | 200 GPa |
Density | 1,760-2,080 kg/m³ | 7,850 kg/m³ |
Corrosion | Immune (no electrochemical corrosion) | Rusts; needs coating/cathodic protection |
Conductivity | Non-conductive | Conductive |
FRP structural design follows FRP-specific standards rather than steel codes, deflection control, not raw tensile strength, typically governs the design.
If You Can Design It, DEFI Can Make It
Our fiberglass products are as customized or as standard as your application requires. We stock common profiles and structures and run a full custom shop for unique projects, whether you need a rigid structural beam like the ones covered in our fiberglass beam guide or an FRP embed angle to anchor grating into concrete.
Contact us today and let’s build it better together.
FAQ
What makes a fiberglass profile “rigid” instead of flexible?
The resin matrix. Rigid fiberglass profiles use thermoset resins (polyester, vinyl ester, or epoxy) that cross-link permanently during curing, locking in a fixed shape and high stiffness. Thermoplastic-based composites stay pliable and can be reshaped with heat, which is why they’re rarely used for load-bearing structural members.
Can fiberglass structural profiles be used as direct substitutes for steel sections?
Not using steel design methods directly. FRP’s elastic modulus (17-50 GPa) is far lower than steel’s (200 GPa), so a profile sized like a steel member will deflect more. Engineers size rigid FRP profiles to FRP-specific design standards, accounting for that difference, as noted on our structural FRP page.
What is the typical service life of FRP structural profiles in corrosive environments?
Vinyl ester pultruded profiles commonly reach service lives past 30 years in chemical, wastewater, and offshore environments, with corrosion rates below 0.001 mm/year. Steel in the same environments often needs repainting every 5-10 years and replacement within 15-20.
What resin system is required for chemical plant and offshore applications?
Vinyl ester is the standard specification for chemical processing, wastewater treatment, and offshore structures because of its superior resistance to acids, chlorides, and moisture. Polyester works for general, low-corrosion construction; epoxy is reserved for the highest mechanical or electrical-insulation demands.
How do fiberglass structural profiles perform under long-term sustained loading?
Rigid pultruded profiles maintain their shape under sustained load because the thermoset resin doesn’t creep the way a thermoplastic would. Design still accounts for FRP’s lower stiffness relative to steel with higher safety factors, typically 2.5-3.0 for buildings and 4.0-5.0 for marine or offshore structures.
What manufacturing process does DEFI use to make rigid structural profiles?
Pultrusion. Continuous fiberglass reinforcement is pulled through a resin bath and then a heated die that cures the resin and locks in the cross-section, angle, channel, I-beam, or tube, without distorting it. That pultrusion process is what makes every DEFI structural profile rigid by design.
