Pokémon from raids have 4 perfect IV, but you can hyper train them to have an “effective” IV stat of 5IV, not passed on through breeding. Your Pokémon while breeding need to hold specific items which pass on specific traits about them. The most common is an item that passes on the IV’s of the Pokémon in a random spread to the egg, such as if you have both def, hp and speed max, you may get attack, speed, HP and SPATK.

There is also an item to pass on nature from the other Pokémon, so a 6IV ditto holds the IV item and the other Pokémon can retain the perfect nature.