Cover Factor

The  figure shows  projected  views  of two  woven  cloths  of  different  construction.  At  A the  warp  and the weft threads  cover  the  area  of  the  cloth  only  partially,  but  at B  the  cloth  area  is  covered  completely  with  no  spaces  left  between  the adjacent warp yarns, and it will be seen that the relative closeness of yarns in a woven cloth is dependent upon the ratio of yarn diameter, d, to yarn spacing, p. This ratio known as relative cover, can be defined as the proportion of a  projected view of a given area of cloth which is covered by threads, and will have a scale from 0 to 1, although it may
also be expressed as percentage cover with a scale from 0 to 100 per cent. 

                               d/p = relative cover,
                              (d x 100)/p = percentage cover 

It  is  preferable  to  express  warp  and  weft  relative cover  separately,  as  the  cumulative  value  of  cloth cover  does  not  indicate  the  comparative  importance  of  each  set  of yarns  which  is  essential  for  the  determination  of  certain  cloth characteristics.

From  the  relationship  shown  above  it  will  be  obvious  that  if d=  p.  the  value  of  relative  cover  is  one,  and  this  is regarded as the theoretical maximum cover. In practice, however, this value can be exceeded considerably in any one direction, either through yarn distortion, or, by forcing the threads into different planes, especially if the relative cover of the opposite set of threads is reduced correspondingly.

The relative cover for one thread system can be calculated as follows by considering an area of 100 x 100mm: 

Area per thread = 100 x d 
Area covered by n threads of one system = n x 100 x d
Therefore, relative cover = (n x 100 x d)/(100 x 100) = (n x d)/100 

Example: The cloth represented at A is specified as follows: Warp — 25 tex cotton, 267 ends/100 mm; weft—36 tex cotton, 334 picks/100 mm. Find the relative warp and weft cover. (Subscript 1 refers to warp, subscript 2 to weft.)