The silicone mask cover I recently bought is useful.

It was inconvenient because sheet masks kept falling off when I dried my hair or walked around. I saw that Daiso sold silicone mask covers, so I bought one and put it over the pack. It prevents moisture from evaporating, and since it hooks onto the ears, it never falls off, making it really great to do housework with the mask on. It's also affordable, so I highly recommend it to anyone who uses face masks frequently.