This cute little gal with her cute little flippers is ready to head to the sea (but not without you, because unlike selkie selkie, she is a mask and not an autonomous sapient being)
The wonder of a copper mask is in the strength and give of the material. Because it is so strong, the mask can be very thin- this makes it both very light, and makes it possible to fit as a second skin. These won't block your peripheral vision the way a leather. paper maiche, or plastic mask would. They can be very comfortably worn all day and night- no worries about sweat or rain causing them to soften and lose their shape. Rinse it with clean water at the end of the night before putting it away. They can stand up to anything you throw at them. As for packing? Throw it in your bag. If you're checking the bag, maybe stuff a balled up pair of socks where your forehead would go. Easy.
Not planning to wear your mask? They won't mind. They can hang flat against a wall, or sit on a shelf.