Q&A: Why does cotton shrink?
Between the Sheets

Q&A: Why does cotton shrink?

Au Lit Q&A

Q: Why does cotton fabric shrink?

A: Cotton fabric shrinks primarily due to the relaxation of the cotton fibers. During the spinning and weaving processes, tension is created as the cotton fibers are straightened, stretched, twisted, and pulled. The heat and agitation in the washing and drying cycles release this tension, relaxing the fibers and allowing them to return to their natural state.

Washing in cold water and line drying to avoid the high temperatures and agitation of the dryer will help to minimize shrinkage. However, there is still a chance for shrinkage.

Recently, Sferra tested a king fitted sheet, following proper washing and drying care instructions. Here is what they found:



Size before washing


84" 18.5"
Size after 1st wash 79" 82" 18"

Size after 2nd wash

78.5" 81" 17.75"

Size after 3rd wash

78" 80.5" 17.5"

Size after 4th wash

78" 80.5" 17.5"

The shrinkage rates were 3.7%, 4.2%, 5.4% for the width, length and depth, respectively. As you can see, by overcutting the king fitted sheet, the post-shrinkage sizing is the perfect fit for the 78x80” king mattress.

Due to this, we purposely overcut our bottom fitted sheets to allow for shrinkage and recommend following formula when purchasing your fitted sheets: 

Mattress Depth + 4" = Fitted Sheet Depth

This will ensure that your mattress is always properly covered.


Information provided by one of our favourite brands Sferra.