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One solution to darken rooms promoted by Kathryn Mewes, a trouble-shooting nanny, is kitchen foil. It's cheap, easy to apply, and can be sourced wherever you happen to find yourself. From a random search result
TOP TIP – Creating a dark bedroom
Many families will have bought a black out roman blind or roller blind but the light will still come in from around the edges.
Sprinkle water over the panes of window glass and press sheets of foil to the windows from the inside. This will stick and remain there for several weeks. Cut the foil close to the frame of the window and this will block out 100% of the light.
[Kathryn] Mewes states she never travels on holiday without her kitchen foil!
I can personally attest that this simple technique does indeed hold foil to glass for weeks at a time. The foil comes away when peeled with no trouble since the only adhesive is water. If any pieces do stick then a damp cloth, or even a damp tissue, will remove.
Upvote:1
Foil is used in most homes in Longyearbyen, Norway, but that's a lot of effort to go through while traveling. I, too, was opposed to eyemasks and now find them invaluable. Bucky brand makes one where the foam bulges out quite a bit so there is no pressure or discomfort on your eyes. I was surprised at how quickly I adapted to wearing one. For ~ $15USD I think it's worth a try. (P.S. I'm merely a Bucky brand fan, not a rep!)