Denier is a term that you see associated with blankets.
You’ll notice that turnout blankets, especially the more expensive ones, generally have a higher denier rating (such as 1200) while less expensive blankets might have a denier rating of 600.
Denier is a way of measuring the thickness or weight of yarn. A higher denier rating means a thicker yarn and a more durable fabric. For example, yarn rated at 1200 denier is twice as thick as 600 denier yarn.
Generally, for horses that live outside or who play rough in turnout generally do better wearing blankets made from higher denier threads. These blankets are heavier and tougher fabrics that are more resistant to tears.
Lower denier blankets are more suitable for situations where there will be less wear (such as stable blankets).
I have to say that my Rambo Wug has lasted for at least 10 years with minimal care on horses that have lived outside 24/7 while I’ve been terribly disappointed with the short useful life of blankets with lower denier ratings.