What is ISOFIX?

Whether you are expecting your first baby or taking on the responsibility of transporting young children for the first time, there are a lot of new things to get your head around – and one of the biggest is sorting out child car seats.

This includes choosing the correct child restraint, knowing the laws surrounding their usage, as well as how you’re going to install it in your car, which is when you’re likely to learn lots of new terms – including ISOFIX.

In Australia, all baby seats must be attached to the car using two methods: the first is a top tether strap and the second is either ISOFIX or the car’s seat belt, but never both ISOFIX/belt at the same time.

ISOFIX capsules operate in basically the same manner as non-ISOFIX capsules, but the big difference is the latter is more prone to forward movement in the event of an impact, being constrained by a flexible seatbelt rather than two fixed metal brackets.

And the big selling point for ISOFIX is that it's foolproof (or as near to that as possible). In the past, as one example, parents have mis-installed non-ISOFIX capsules by wrapping the car's seatbelt around the seat with the baby already occupying it, rather than threading the seatbelt through the hoops at the rear of the capsule. An ISOFIX capsule is just 'point-and-click' to lock it in place.

ISOFIX was invented in the late 1990s in Europe as a system for attaching a child seat to a passenger vehicle without using the seat belt.

It did, however, take a long time for them to be approved for use in Australia, with the green light finally coming in 2014.

ISOFIX anchorages are two metal bars that are built into the vehicle during its original manufacture for attaching the child seat to the car. These lower attachment points act as an alternative to the seat belt.

It is to these anchorages that you attach the ISOFIX connectors of a compatible child seat.

You’ll find an ISOFIX connector on each side of your child seat, near the base (sometimes tucked away underneath). They look a bit like a lobster claw!

In most five-seat family cars there are ISOFIX anchorages in the two outer rear seats, clearly labelled with the ISOFIX symbol.

Some ISOFIX anchorages are within plastic guides, or behind elaborate covers. Others are just bare or concealed in the gap between the backrest and seat base cushions.

Adjusting the ISOFIX anchorage points for a secure fit

Once the child seat’s ISOFIX connectors are securely attached to the car’s ISOFIX anchorages you must adjust them for a secure fit.

Some child seats have rigid ISOFIX connectors on a ratchet-type system where you push the child seat against the vehicle’s backrest until it is firmly in place.

That said, most child seats sold in Australia have straps.

For example, ISOFIX-compatible Infasecure child seats have a colour indicator on them that turns from red to green to let you know when you have tightened the strap enough.

ISOFIX was designed to minimise user error when installing child seats and to make installing child seats easier.

In some cases, ISOFIX can be easier to use than the seat belt, while in other cases it can be more difficult to use than the belt. It depends on both the car and the child restraint.

Usually, when there are one or two child seats installed in a car, then the ISOFIX is easy to use.

Often when you add a third child seat in the central position the seat belt is a better option, giving you a bit of freedom to position the outer two child seats slightly further apart to allow room for the third in between.

Not all child seats have ISOFIX attachments for a couple of reasons.

Firstly, on some child seats you will get a more secure install using a seat belt due to their shape or style.

Secondly, ISOFIX is only rated up to 33kg. This means ISOFIX can only be used up until the combined weight of the seat and the child reaches 33kg.

That 33kg limit includes the child seat plus the weight of the child, so a lighter seat allows for a heavier child. Most ISOFIX child seats suggest use until the child weighs 18kg, after which you must use the vehicle’s seat belt to secure the child seat.

Child seat types E, F and G are not available with ISOFIX as an option. This is because they are designed for use by children aged four to eight and four to 10, so the combined weight of the child and seat will exceed 33kg.

Hopefully, that’s given you an overview of ISOFIX and some key things to consider before transporting young children.

In the coming weeks, we’ll nominate some of our top picks when it comes to passenger cars and SUVs that do ISOFIX really well – and also those that cater for more than just the two outboard rear seat positions.

ISOFIX was jointly developed by Volkswagen and child safety capsule manufacturer Britax-Römer. The first products compliant with ISOFIX went on sale in 1997.

If the old-style capsule is in a fit state and correctly installed, it will be as safe as an ISOFIX seat. But be aware that capsules and their restraints can degrade over time, and it's recommended to replace the capsule after six years.