The better you care for your silk, the better it'll care for you!
For long lasting silk, the best method is hand washing inside out in cool water with a delicate-only detergent. Just swish the fabric around in the basin, not scrubbing or wringing the fabric. To keep your silk's beautiful sheen, after washing and rinsing do a second quick soak in white vinegar then rinse thoroughly. Lay your silk on a towel to soak up excess water then lay flat to dry. Iron on low heat if desired.
If you choose to machine wash, turn your pillowcase inside out and use a delicates-only detergent and a mesh delicates bag is handy for your silk masks & hair accessories. Always use cool water on the most gentle cycle and do not wring out your silk item. Adding white vinegar to the rinse cycle will bring out your silk's natural sheen. Use a towel to absorb extra moisture then lay flat to dry. Keep your silk out of direct sunlight while drying. Iron on low heat if desired.