Pomade and serums are suppose to be used on hair that is 100% dry, to finish your look:
After flat ironing, rub a small amount of pomade between hands.
Rub into hair, starting at ends and working up to the roots.
Smooth pomade/serum over the ends, fly aways and surface of your dry hair.
I Know I read that flat ironing, after pomade/serum was applied to hair, is not healthy for the hair because it can cause hair to become dry/britle over time.
Unfortunately, I can't recall where I heard that to make a reference.
Sometimes, we can be creative and find a new way to make a product work better. A stylist dried my hair, used spray wax on my hair, then flat ironed.
My hair was so straight it was incredible!
But everyone told me that spray wax is not meant to be flat ironed.
OSIS Sherbert spray wax, by the way.
Hope my info helps