Straight from the horse’s mouth, figuratively:
For the consumer, the best way to shrink any cotton article is to tumble dry. The unrestricted mechanical action in the dryer allows the construction of the article to fully relax.
Our studies have shown that washing and drying 5 times will completely remove any residual shrinkage.
In your case, to reduce the cost of repeatedly drying a canvas rug, our suggestion is to wash the rug and then hang dry until it is almost dry but damp to the touch. The complete the drying in the dryer with heat. After you do this three times, most all of the shrinkage will be gone.
Thank you for contacting Cotton Incorporated with your cotton questions.