The percentage of silk per square inch of a 22 mm silk is almost 20% higher than that of a 19 mm silk. The higher momme weight also implies that the weave is denser, and this denser weave helps to protect the sheen and luster of the silk. This gives room for stronger durability.

For Hand wash which is always the best and safest method for washing particularly delicate items like silk
For machine wash, there is more risk involved, and certain precautions must be taken to minimize them