A GRP enclosure is a weatherproof cabinet moulded from Glass Reinforced Plastic — fine glass fibres set in a polyester resin. The result is a housing that's light like plastic but strong like metal, and that simply doesn't rust, rot or need repainting. They're the green and grey cabinets you walk past on every UK street housing electrical supplies, meters, telecoms gear and water standpipes.
GRP, FRP, fibreglass — same thing?
Near enough, yes. GRP (Glass Reinforced Plastic) is the usual British term. FRP (Fibre Reinforced Plastic/Polymer) is the international term, common in American datasheets, and technically covers other fibres too — but in enclosures it almost always means glass. Fibreglass is the everyday word for the same material. If a spec sheet says any of the three, you're looking at the same family of material.
How a GRP enclosure is made
The cabinet is built up in a mould: first a gelcoat — the pigmented outer resin layer that gives the finished surface its colour and UV resistance — then layers of glass fibre laminate bonded with resin. Because the colour is in the gelcoat itself rather than painted on, scratches don't expose bare metal and the finish lasts decades without maintenance. Fire-retardant resins can be laminated in where the specification calls for it.
Why it suits electrical equipment
Three properties do the heavy lifting. GRP is non-conductive, so the housing never becomes part of a fault path and needs no earthing of its own. It is corrosion-proof — coastal salt, road spray and rain do nothing to it. And it has an excellent strength-to-weight ratio: a kiosk that two people can manoeuvre into position will still shrug off the knocks of roadside life. The full case is on our Why use GRP page, and if you're comparing materials, see GRP vs steel enclosures.
Where you'll find them
Everywhere infrastructure meets weather: electricity supply and distribution cabinets, feeder pillars, metering, rail and telecoms equipment, EV charging infrastructure, pumping stations and water treatment works. Sizes run from wall-mounted boxes through floor standing cabinets to walk-in kiosks you can stand up in.
Ready to look at actual cabinets? The whole range is organised by mounting style on our GRP electrical enclosures page.