Child in Britax Advansafix car seat
The rules for using a child’s car seat can seem complicated at first. CREDIT Britax

The laws around using child seats or baby seats in cars can seem a little confusing, not least because not all car seats are compatible with all cars. This is one of the major reasons for the introduction in 2013 of a standard of seat called iSize, one of the key principles of which is to create a standard fitment across all makes of car seat and all models of new car.

However, while iSize seats are now widely available, they are not the only option. Rather, they are sold alongside the traditional European standard of car seat, known as R44. In this guide we’ll explain the differences between the two, as well as the role Isofix plays in improving infant safety.

What is iSize?

It is likely that at some point iSize (known technically as ‘R129’) will become the only option of car seat available to buy. However, even if that happens you will still be allowed to use seats built to R44 guidelines if that’s what you already own.

In addition to standardising how the seats are fitted, iSize differs from R44 because you choose the seat depending on a child’s height, whereas with R44 selection is based on his or her weight.

iSize also always uses a five-point harness and promotes having children rear facing for longer due to the added crash protection this gives their still developing bodies. As such, with iSize children must be kept rear facing until at least 15 months old.

Older child in Britax Advansafix i-Size car seat

What is R44?

The other option when choosing a car seat is to buy one where its size is dictated by the baby or child’s weight. These R44 seats are also available as rear or front facing (including rear-facing seats which will take them up to age 4), but rather than insisting on a five-point harness, the child can also be strapped in with a seatbelt or what is known as a safety shield. This is a separate segment of the seat that slots in over the child’s lap and is then held in place with the seatbelt.

Babies and children weighing less than 9kg must be rear facing according to R44 regulations, although it’s widely accepted that even this is rather early to switch to front facing. Waiting until the child is 13kg (or, as with iSize, 15 months) before putting them in a front-facing seat will help ensure their neck has a better chance of supporting their head in a crash.

To help you identify what type of R44 seat is correct for your child, there are categories ranging from Group 0 to Group 3 to choose from.

Car Seat GroupChild's WeightType of Seat
00-10kgLie-flat or rear-facing baby seat with harness
0+0-13kgRear-facing baby seat with harness
19-18kgRear- or forward-facing baby seat with harness or safety shield
215-25kgRear-or forward-facing child seat with harness, safety shield or seatbelt
322-36kgRear-or forward-facing child seat with harness, safety shield or seatbelt

Isofix Explained

Britax Romer Evolvo Isofix car seat in purple
Isofix mounting points help you clip a child seat safely into a car. CREDIT Britax

No matter what class of class seat you choose, chances are it will come with Isofix. But what is it?

Put simply, Isofix is a means of securely attaching a car seat to a car, and thus dramatically reduces the chances of a seat being incorrectly fitted. It involves clipping a pair of extending arms that are attached to the child seat on to two mounting points at the base of the car’s rear seats (some cars have Isofix points on the passenger seat too). These arms combine with either a support leg or a top tether that hooks to an anchor point behind the headrest, both of which are designed to stop the seat tipping forwards in a crash.

Isofix can be included on the seat itself, or on a separate base unit that the seat clips into, the latter being more prevalent on baby seats that work as part of travel systems.

Top Tip: You might assume that an Isofix car seat is compatible with any Isofix-equipped car, but that is not necessarily the case. Car seat manufacturers do however provide a list of approved vehicles, and if you’re still unsure a good car seat retailer will be able to advise.

Other Point to Consider

  • When looking for any car seat you’ll want to know it conforms to EU safety standards. To do this look on the label for a capital E in a circle.
  • If you must buy a car seat second-hand make sure it’s from a trusted source and can be 100% relied upon to do its job. Best practice therefore is to buy new if at all possible.
  • Children need to be in a car seat until they are aged 12 or taller than 135cm. Fail to do this, or put them in a seat that is not appropriate for their age, weight or height, and you will be breaking the law.
  • The safest place for babies and children to travel is in the back of the car. If you do need to carry a rear-facing child seat in the front of the car it is vital to turn off the passenger airbag. The switch for this is usually located in the glovebox or passenger-side door frame.
  • Carrying a forward-facing child seat in the front is also not recommended due to the force with which an airbag deploys. If you need to do this leave the airbag switched on but slide the passenger seat as far back as possible.
  • Studies have shown that traditional booster seats without any back or side support do not perform well in the event of a crash. As such, you can only buy such seats in the R44 group 3 category.
  • Even when you have a compatible car and child seat it is possible to make mistakes during installation such as having straps positioned at the wrong height, or not moving a car’s headrest out of the way. As such it is important to always read the manual for your particular child seat, and if in doubt ask an expert at a respected car seat retailer for advice.


Read Questions From Parents and Grandparents

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