Cybex Base G3 360° Rotating ISOFIX Car Seat BaseCYBEX Base G3 i Size ISOFIX Car Seat Base One Base, Two Seats The CYBEX Base G3 i Size is the ISOFIX base designed to work with the CYBEX G3 Modular System, offering a long term solution that grows alongside your child from birth to approximately four years old. Compatible with the CYBEX Cloud G3 infant car seat and the CYBEX Sirona G3 toddler car seat as well as the previous generation Cloud G i Size and Sirona G i Size the Base G3 is built around