A plied yarn is a yarn made up of two or more finer yarns. Weaker yarns are combined together to create one stronger yarn. Rope is a good example. Although oversized compared to fine yarn, it uses the same principle. Plied yarns do not necessarily produce a stronger yarn. It takes more, shorter fibres spun together to make a yarn with the equivalent strength of one made up of longer staple fibres. Fabrics woven from plied yarns have a different finish to those of quality, long staple yarns.
Bed linen companies have cleverly and carefully been able to market their products as a higher thread count, by weaving fabrics with plied yarns. Some companies then count each yarn inside the plied yarn to create a higher and misleading thread count.