The izi up x3 fix is basiclly the same booster seat as izi up x3 with the added option that it can be fitted using the cars isofix points this ensures that the car seat always is fixed in the car and will not move around in the event of a collision when installed with isofix the izi up x3 fix enables the innovative side impact protection feature sir offering even greater side impact protection side impact protection sir the izi up x3 fix includes this extra feature sir side impact rot