Unknown birch species for collecting bark

I have seen some unusual birch trees today. I have never seen this type anywhere else, so I assume the trees are not native and have been planted for decorative reasons. They caught my eye because they have an almost flawless white bark. This is in striking contrast to the usual birch (betula pendula). The best thing about this unknown birch is that it sheds layers of the bark on its own. I have collected some patches of it, but it seems that I am too late. Most of the trees have fresh bark without any signs of exposure to wind and weather. Maybe shedding season is already over. Or does it happen all the time? Does anyone know this birch species?

Daniel