Poppy! I like that. In answer to your question, NO, the hoses do not leak due to porosity (50 years ago maybe, but not now). The hoses leak at the connections, usually due to failed "O" rings, and sometimes due to corrosion of the metal coupler. The "Freon", which is a regestered trade mark of DuPont (like Kleenex), is what folks generically call A/C refrigerant. Refrigerant is a chemical compound and in its gasous state is very fine (from a molecular point of view) and it will leak out of any weak seal. I have a daughter in law that is a chemical engineer for a world class automobile manufacturer. She is one of a select few engineers responsible for ANYTHING chemical that goes into making one of their automobiles. We have great discussions about such things.