The number of knots per square centimetre ranges from 20  30 for a coarse wool carpet to 100  200 for the most expensive silk carpets, which can cost tens of thousands of pounds.
Silk carpets require more knots to hold them together. 
mnli hypothesis: Silk carpets require more knots to hold them together.  premise: The number of knots per square centimetre ranges from 20  30 for a coarse wool carpet to 100  200 for the most expensive silk carpets, which can cost tens of thousands of pounds.