5 ply (Guernsey) Traditionally used to knit fishermen's clothing.
Double knit Double knit or DK is the most commonly-used ply of yarn. It can be used for everything from baby clothes to men's jumpers and is available in a wide range of colours and textures.
Aran Typically for warm cabled garments, currently having a resurgence in popularity.
Chunky A thick yarn which is quick to knit, also suiting beginners. It is typically used for hats scarves and jumpers.