  We introduce a general construction that takes as input a so-called stiff PRO
and that outputs a Hopf algebra. Stiff PROs are particular PROs that can be
described by generators and relations with precise conditions. Our construction
generalizes the classical construction from operads to Hopf algebras of van der
Laan. We study some of its properties and review some examples of application.
We get in particular Hopf algebras on heaps of pieces and retrieve some
deformed versions of the noncommutative Fa\`a di Bruno algebra introduced by
Foissy.
