The "300 son" does not mean anything, it is a marketing technique dune to convince consumers of the product quality.
"The more son to the square inch, the higher the fabric is durable. There is a misconception that by against the more son thumb, the larger the sheet is quality. However, everything depends on the quality of the wire and in the same fabric construction. A high amount of son thumb might give a more rigid and durable cloth, but not necessarily more comfortable. " Preview: legitimedepense.telequebec.tv
In short, I use extra sheets.