Yes, they are spring loaded (in the barrel) just like the patio awning. The weight of water, snow, ice, pulls more material off the roller. As the weight is removed (evaporation, wind, broom, etc.) the spring rolls the material back into the tube. On ours this is most noticeable on the long awning over the living room slide. I suppose if water sat there long enough it could mildew but I haven't worried about it. Sometimes after a heavy rain we will look out a slide-end window just as the wind gusts and water pours off that awning.
Some folks use a ball or other method to either tent the awning or pull it down ('v') in the middle to keep the water from pooling. That's an option if you want to do that.
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