Thread count has become a meaningless term used by marketers to encourage you to buy the product.
According to Choice magazine, many manufactures count plies not threads, in order to make their thread counts sound more impressive (so a 300 thread count construction made with 2 ply yarns would be called a 600 thread count).
The Fair Trade Commission has recently ruled that plied yarns should only be counted as one thread when calculating thread count, not individual strands. Unfortunately, this is not enforced and still occurs on a regular basis.
The new trend
In order to achieve higher threads counts in a more technically correct manner, manufacturers have moved to using single ply threads with multiple picks added to the weft. Some sheets have as many as 8. This practice increases thread count but otherwise has no practical or useful purpose. It can actually have an adverse impact on the quality of the fabric, making it feel heavy and decreasing its durability over time.
The other problem with multiple pick insertions is that they are often done with short staple cotton of inferior quality. This leaves the fabric prone to pilling and slippage. Additionally, the pick may not be properly integrated into the weave, which causes the fabric to become unstable. The fabric may feel soft at first, but after a few washes it is likely to be prone to abrasion and uneven wear.
It can be argued that in weave quality terms alone, the best fabric will be made with single ply yarns and have a single pick, that is, one warp thread and one weft thread. The highest thread count you can achieve with this type of construction is 380. Sheets stating higher thread counts have to be using double-ply yarns or multiple picks, which results in a rougher, heavier sheet.
