The present invention relates to imidazoyl urea polymers and their use in aqueous acidic plating baths for metal or metal alloy deposition such as electrolytic deposition of copper or alloys thereof in the manufacture of printed circuit boards, IC substrates, semiconducting and glass devices for electronic applications. The plating bath according to the present invention comprises at least one source of metal ions and an imidazoyl urea polymer. The plating bath is particularly useful for filling recessed structures and build-up of pillar bump structures.