The i-Size certification (officially ECE R129) is the latest and most stringent European standard for car seats, introducing a classification based on the height of the child instead of the weight. It requires mandatory side impact tests, encourages longer rear-facing use and requires ISOFIX for a more secure fit. Seats designated as i-Size offer a higher level of safety and better adaptation to the child's physiological development. It is recommended to choose car seats with this certification if the vehicle is compatible.