Why did the Yelnats apartment smell of food odor and burning rubber?

The Yelnats apartment smells like foot odor and burning sneakers because of Stanley's father's attempts to invent something.
Stanley's father is convinced that he can find a way to recycle old sneakers. This means that he has to find a way to break down shoes that have been worn—from which comes the scent of foot odor. He also has to find a way to break down the rubber soles of the shoes. It's clear that there are probably many shoes in the apartment and that he has tried to use heat to recycle them.
He says that the first person to find something to do with these old sneakers will be a rich man. Of course, this experiment is why Stanley is later arrested for stealing old shoes and sent away.