The accreditation, awarded earlier this month, saw the finishing equipment manufacturer promoted from a "very good" rating in its 2010 assessment to "excellent" in 2012.
Assessments and interviews with around a third of the 65-strong UK team on their professional experience at Duplo resulted in the Surrey-based company being commended for its "good family ethos" and "management effectiveness".
Duplo head of HR Jane Doyle said: "IIP provides us with a means to benchmark ourselves amongst the best run organisations in the country.
"The most important resource a business has is its people. IIP shows us how to get the most out of this resource and ultimately helps us maintain our position as a leader in an ever more competitive industry."
Duplo, which is hosting its annual showcase London Calling Rocks next week, was also recognised in the Sunday Times Best Companies list in February, focusing on its leadership strengths and wellbeing of its staff.
Doyle added: "Ultimately all these initiatives are about fostering an environment where people are proud to work, feel a sense of empowerment and helps them be effective in their job."
