winter watering with bubble wrap

When winter days only warm to 50 °F, my floating plastic straws or Scotch Brite pads did not protect the bees from drowning.   In my disappointment, I tried to imagine something better, perhaps plastic straws and bubble wrap.   Even more simple...I'm using one layer of bubble wrap with the smooth side down.  I cover almost all of the water source with bubble wrap - works great!