What could my father possibly be downloading to make the internet this slow?

Whenever my mother is gone the internet drops speeds as if we were back to 1995. My bf who has an AS in computer science says my father must be downloading some serious stuff to make it go this slowly. He has all of the expansive internet stuff (I don't know much about it) a new router or w.e that's supposed to be top notch, and I KNOW he has something maybe another one in his room because his internet ALWAYS works! I'm not on the internet a lot, but when I am I expect it to work and since he's been laid off for a year now all he does is go on facebook and whatever it is he is downloading (My bf says he's downloading something but no one knows what he's really doing) what do you think it is?