Our barn has curtains. They're made of plastic, and they roll manually with a crank. They're two separate curtains, so you can open them from the bottom up or the top down.
This way, it can be wide open in the summer for optimum ventilation, and closed up tight in the winter to make it warmer. The semi-transparent plastic allows the sun to shine through so it's still bright year-round.
These are common in lots of new barns, but if you didn't know what they were, you might think the barn was unfinished - since plastic on a house indicates it's still under construction.
But these curtains are here to stay! And since it's Fourth of July weekend coming up, hopefully they'll be wide open ... I love a holiday weekend of good weather. Also, that way, the calves might be able to glimpse a little of the fireworks.