Gel eye mask: you stick it in the fridge for for an hour, then put it on your eyes when they are tired and/or swollen.
The one in the kit is also silk, so it breathes.
BA gave us silk sleep masks, terry tube socks, and a small toothbrush with a tiny little tube of toothpaste. I liked it.
Thanks for the explanation!
I don't remember BA silk eye masks. But the first time I flew with them I was pretty new to travel and didn't keep anything of the kit (I do remember the socks, toothbrush and toothpaste though). The second (and last so far), I would have kept the mask but I seem to recall it was plastic and thus worthless to me.