Are sheets at the window a real alternative to shutters and blinds?

Do curtains and sheets help prevent the warm sunlight from entering the apartment on hot days? It's better than nothing, say experts. Photo: Jens Kalaene/dpa-Zentralbild/dpa

What's the best way to keep the heat out on a hot day? According to experts, it's roller shutters. But unfortunately not every building has them, and installing them can be expensive.

Is putting up a sheet in the window or the balcony door a real alternative for renters?