Protects well, the quality of the material is OK and workmanship is OK too, for the price I found very good. I bought the size of 13.3 inches and it fit my notebook well (which is dumbed down, it's 13.3 inches, so just buy the right size).
OBS: it is in fact impervious from the outside, but only against rapid spillage, if the liquid is stopped for a while on top it ends up absorbing. That is, if you spill a glass of water on top without meaning it's good, don't wet it in, but if water bottle opens inside the backpack and stay for a while it will get wet in the same way.