As far as linens or any fabric is concerned, the term TPI refers to Thread count per inch. It is an important factor you need to take into account, while buying a bed sheet; the higher the TPI of a linen, the softer and more comfortable it becomes and lasts long too. Those with less than a TPI count of 200 are not recommended for daily use as the wear out faster. TPI stands for "threads per inch". In fact the linen will have both a warp TPI and a weft TPI, textile terms for the threads in the vertical and horizontal planes. The higher thread count is preferred as the fabric is finer and smoother.