Fiberglass (sometimes spelt fibreglass) is a composite material made from resin/plastic re-inforced with fine fibers of glass. The result is a very strong, durable material capable of withstanding climatic adversity (frost-proof) with the added advantage of being comparatively very lightweight. This makes a fiberglass planter an ideal choice if you plan to move your planter around. Fiberglass is also non-porous and therefore retains moisture, which means that it withstands the heat better than other materials such as terracotta because it stays cooler. For garden planters to be used outside (but not planters for indoor use), it is desirable to have a drainage hole for excess water.
Our sister site CrinkleCrankle sell an excellent range of Fiberglass Planters, with free delivery throughout the UK.
See blog posts on the use of fiberglass in gardens: