The number 1 indicates poly(ethylene terephthalate), or PET. PET is the material most often used in water or soft drinks bottles, as well as other food containers such as pots, tubs, oven-ready trays or jam jars.
When PET is recycled it can either be used to manufacture more drinks bottles (this is known as closed loop recycling) or spun into fibres to make textiles. Clothes made from PET are more common than you'd think; when PET is used by the fashion industry it's generally known as polyester.
The number 2 symbol is used on high-density polyethylene or HDPE. HDPE is a tough material that is easily blow-moulded and stands up well to low temperatures - qualities that make it ideal for use in milk jugs and detergent bottles. It's also used for things like tupperware, children's toys, chemical drums and cable insulation.
HDPE is the most-often recycled material in the world, and is used in everything from street furniture to stationery products like rulers. Many Glasdon products made from recycled materials contain a large amount of post-consumer HDPE material.
Number 3 is used on a plastic most people have heard of: polyvinyl chloride, or PVC. PVC is commonly used in the construction industry for window frames and water pipes, as well as cling film, synthetic fabrics and even your credit and debit cards.
The European PVC industry body VinylPlus reports that 257,084 tonnes of post-consumer PVC was recycled in 2011. 75% of collected vinyl is used to make flooring (source: http://www.recovinyl.com/).
Low-density polyethylene (LDPE) is marked with the number 4. LDPE was the first grade of polyethylene (also known as polythene) to be produced. It's more flexible than HDPE, and as the name suggests, the molecules are lower density. LDPE is most used for the production of plastic carrier bags, and laminated into paperboard as part of Tetra-pak style containers.
LDPE degrades during the recycling process, so closed loop recycling is not as common. Recycled LDPE material can be used in carrier bags or laminated as described above.
Polypropylene (PP) is number 5, and is used in the manufacture of bottle caps, packaging film (PP film is the very smooth kind you find wrapping products like CDs, confectionery and even cigarette packets), CD and DVD cases and a range of household products.
Polystyrene (PS) is marked with a number 6, and has many more uses than you might expect. When most people think of polystyrene they picture the expanded polystyrene (EPS) foam used in packaging - either shaped to hold a product in a box, or as the "packing peanuts" that explode out of cardboard boxes.
Sheet or rigid polystyrene is used in all sorts of applications where low-cost plastics are needed: disposable razors, CD "jewel" cases, disposable cutlery and smoke detector housings are just some of the many uses for polystyrene.
Recycling of polypropylene and polystyrene is only just becoming widespread in the United Kingdom: while polystyrene is easily recycled, its low weight makes it very low value by volume, giving recyclers little incentive to collect it compared to, for example, metal products. Polystyrene in the form of Styrofoam cups is a particular environmental problem, with the United States EPA (Environmental Protection Agency) estimating that 25 billion are sent to landfill in the US every year.
Ultimately, the kinds of plastic you can recycle in your home or office will vary depending on your service provider. While the number of local authorities collecting mixed plastics is rising (we estimate as many as 50% of councils will now take most plastic products), the remainder still only take clean drinks bottles - PET and HDPE.
Residents of England and Northern Ireland can input their postcode at http://www.recyclenow.com/ to learn more about recycling collections in their local area. For Scotland, please visit http://www.recycleforscotland.com/recycle.asp and in Wales use the recycling locator at http://www.wasteawarenesswales.org.uk/.