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In a GRP profile the glass fiber carries the load; how the profile stands up to its environment is largely set by the resin. We pultrude in three resin systems — orthophthalic and isophthalic polyester and vinyl ester — each of them also available in a flame-retardant grade.
In a pultruded GRP profile two materials do two different jobs, and it is worth being blunt about which does what before anything is specified.
The glass reinforcement runs continuously along the length of the profile and takes the load. Tensile strength along the axis, bending stiffness, how far a section sags over a given span — that is fibre work, decided by how much glass there is and how it is arranged. Swapping the resin does not make a profile stronger.
The resin is the matrix around that glass. It wets the filaments out, transfers shear between them, holds the section true as it cures, and forms the outer skin that meets the world. So the resin decides the things that show up years later: resistance to chemicals, behaviour at temperature, water uptake in permanently wet service, how the surface holds up under ultraviolet light, and how the material is assessed when a fire specification is written against it.
The practical consequence is easy to state. Two profiles can share the same section, the same wall thickness and the same weight per metre, and still have very different service lives — one on a dry indoor cable route, the other in the splash zone of an acid dosing line. The section number does not change. The resin letter does.
That split is also why the general material pages sit alongside this one rather than repeating it: what a GRP profile is covers the make-up of the laminate, mechanical properties covers the load side, and this page covers the environment side.
An earlier version of this page said we offer a single general purpose polyester. That was wrong, and it understated what is actually on the production programme. We pultrude six resin systems, and they are six separate product codes rather than options to be negotiated at order time.
The same section number means the same dimensions and the same weight per metre in every one of the six. Only the letter in the middle of the code moves, which is what makes the choice a specification decision rather than a redesign.
↳ settle the environment first, the section second
This is the default, and for a great deal of work it is the correct default rather than a compromise. Indoor framing, walkway and platform supports, cable routes in dry buildings, guards, trims and general fabrication — anywhere the profile meets air, occasional water and normal temperatures rather than a named chemical. Reaching for a heavier resin here spends money on a risk that is not present.
Move up to isophthalic when the profile will be wet more or less permanently, or when the atmosphere itself is loaded: coastal and marine air, wash-down areas, pump rooms, uncovered outdoor structures that stay damp, splash from clean or lightly contaminated water. Isophthalic grades hold their surface better under sustained moisture, and they are the sensible middle step before paying for vinyl ester.
Vinyl ester answers a named chemical, not a general worry. Acid and alkali contact, dosing and dilution areas, electrolysis and plating halls, effluent channels, chemical storage bunds, the aggressive ends of water and wastewater treatment. It is the most expensive of the three, so the honest advice runs both ways: use it where the exposure is real, and step back to isophthalic where it is not.
If you are not sure which of the three bands you are in, that is a normal question and not a sign of a badly written specification. Send the substance, its concentration and the service temperature and we will place it for you.
The uncomfortable part first. A glass reinforced polymer is an organic material and it is combustible. A flame-retardant resin does not turn it into a non-combustible product, and anyone who tells you otherwise is selling rather than engineering.
What an FR formulation does change is behaviour. Ignition is harder, flame spread across the surface is slower, and the material tends to stop burning once the flame source is removed rather than sustaining itself. In a real building that difference is the difference between a contained incident and a spreading one, which is precisely why fire specifications exist and why the grades are worth having.
Those specifications are written against reaction-to-fire test standards rather than against material families. In Europe the usual reference is EN 13501-1, which sorts construction products into Euroclasses on the basis of a set of reaction-to-fire tests. In North America the common reference is ASTM E84, a tunnel test that returns a flame spread index and a smoke developed index. Both describe how a specimen behaved in a defined test on a defined build-up; neither is a property you can read off a resin name.
Our position is the same here as everywhere else on this site. We will tell you which resin systems we produce and what they are formulated for, and we will not imply a classification we do not hold. If your specification names a Euroclass or a flame spread index, put it in the enquiry at the start and we will tell you plainly what we can and cannot support. The quality, standards and testing page sets out exactly where that line sits and why we draw it there.
Our codes are built so that a resin can be specified in a single character. The pattern is CP{section}-{resin}-{number}:
So CPU-O-106 is a 75 × 32 × 5 mm channel in orthophthalic polyester. CPU-V-106 is that same channel — same dimensions, same weight per metre — in vinyl ester. CPU-VA-106 is the vinyl ester version in the flame-retardant grade.
This matters at order stage. Write the resin into the code on the purchase order and there is nothing left for anyone to interpret later: not the buyer, not our production planning, not the person unloading the lorry. It is the cheapest piece of quality assurance available on the whole job.
A common shortcut in enquiries is to treat ultraviolet resistance as a resin question. Mostly it is not. Weathering is handled at the surface, by a fine veil applied as the outermost layer during pultrusion. That veil leaves a resin-rich face over the structural laminate, which keeps ultraviolet light off the reinforcement, keeps the surface smooth and makes it easier to clean.
The two choices stack rather than substitute for each other. A vinyl ester profile in a treatment plant still benefits from a veil on the faces that see daylight; an orthophthalic profile with a good veil is often the right answer for an outdoor guard that never meets a chemical. Take the resin from the environment inside the material, and the veil from the environment on its surface.
The surface veil, UV and fire page covers the surface side in detail, and the pultrusion process page shows where in the line the veil is introduced and why it cannot be added afterwards.
You do not need to arrive with a resin already chosen; placing it is our job. What helps is a short description of where the profile lives: the substance it contacts and its concentration, the service temperature, whether it is wet continuously or intermittently, indoor or outdoor, whether ultraviolet exposure is constant, and whether the project carries a fire specification. Add the section you have in mind, or the span and the load if you have not chosen one yet, and we will settle the resin and the section together. The applications pages show how those decisions have gone on comparable jobs.