My old inflateble has become porous. It's made of the neoprene, not hypalon.
Have heard about some liquid that impregnates the rubber from the inside.
One is supposed to sip it into the chambers. Please if anyone knows where to
find it (web address). Any experience?
Thx in advance.

Almost sounds like that Fix-a-flat junk they sell in auto parts stores. Fix a
flat is "Temporary use only".

You really want to trust your life to a can of rubberized Cheez Whiz?

You really ought to consider replacing a dinghy that is so old that it has
become "porous".

Lots of swap meets this time of year. Probably pick up something for a few
hundred bucks, and it would have to cost at least a hunskey to have anybody do
any sort of skilled job of pumping miracle goo into your old boat. :-)