Beehives have been made by Man out of a very wide range of materials. Straw, clay and wood have been perhaps the commonest materials in use throughout history but other materials have also been used, including concrete, but the alternative material which was found to be most successful was plastic. A relatively small number of hives are made out of solid plastic, which has the advantage of being easily cleaned and can be moulded into complex shapes, but on its own it lacks thermal insulation, unless made with twin walls with a cavity between them. However, the most numerous and successful of the new hives are made from forms of plastic which have been expanded or foamed to give both rigidity and high thermal insulation.
Polyurethane foam produces very hard wearing hives as the material, when injected into a mould, naturally forms a smooth outer surface, sandwiching the polyurethane foam between a hard outer surfaces which require no surface treatment. However, the disadvantage of polyurethane foam hives is their high cost compared to the rival material - expanded polystyrene (EPS). For a short time in the 1970's a polyurethane foam National hive, called the "Honey Home" was produced. Details accessed from the button top left. R.P.
EPS is very commonly used in packaging , a role which does attract some adverse environmental comment, but it is also very commonly used as insulation in buildings, usually sandwiched between outer surfaces of wood or metal.
The EPS used in packaging and insulation typically has a density of between 20 and 50 kg/m3 which is a density which gives high thermal insulation, but lacks any significant mechanical strength.
EPS Hives - "Poly Hives"
The EPS used for the manufacture of beehives should normally have a density of at least 100 kg/m3, at which density the material is significantly stronger than the packaging materials most readers will be familiar with. A good test of an EPS beehive is to stand on the roof - if it can take your weight it will be strong enough for your bees. Although the higher density gives structural strength, the main reason for stipulating a density of 100 kg/m3 is because anything less can and will be chewed by the bees.
EPS hives, usually referred to as "poly hives", were invented in Europe in the 1970s and are now very widely used. A Danish equipment supplier has been quoted as saying that today 99% of all new hives sold in Denmark are made from EPS. The situation is similar in other parts of Northern Europe and poly hives are also widely available in the USA and a number of other countries.
A limiting factor on the wider use of poly hives is the large variety of different frame sizes used by beekeepers in different countries and the high cost of producing the tooling for moulding the hives. The Langstroth is not surprisingly the hive format most represented by poly but poly hives in unique national formats are now beginning to appear. In the UK there are now a number of suppliers offering poly hives in the common B. S. National size, both standard and 14 x 12 being available.