Both are approved regulations (the "R" stands for regulation) that car seats can be sold under in the UK. R129 is also known as "i-Size" and is the newest regulation that includes side-impact testing, improved head and neck protection, and extended rearward facing. R44 is an older regulation, but still requires products to go through rigorous testing and safety standards. R44 is being phased out in the EU, but not in the UK. We offer car seats following both regulations to give our customers a wide range to choose from, for all budgets.