What is an Isofix Car Seat | All You Need to Know 2020

Posted by Julie Monson on

What is an ISOfix Car Seat

Julie Monson Car Seat support South Africa

Julie Monson
Occupational Therapist and car Seat Support South Africa founder.

What is an Isofix car seat?

ISOfix is an alternative way to secure a child's car seat instead of a seat belt. ISOfix covers both Infant (Group 0/0+) and toddler (Group 1) seats. The mechanism for attaching the seat is two "crocodile-like" clips that connect the car seat to two lower u-shaped metal anchors which are mounted to the chassis of a vehicle. The size of these u-shaped brackets is regulated by the International Organisation for Standardisation.


ISOfix was devised by the manufacturers of child restraints in order to get their products to work effectively in as many cars as possible, as the three point seat belts in vehicles vary substantially and parents were installing their seats incorrectly. The ISOfix system was developed jointly by Britax-Romer and Volkswagen and was implemented in the USA in 2002 and in Europe in 2004.

Are isofix car seats safer? | ISOFIX VS BELTED

When a car crashes it stops suddenly, but the child car seat and its passenger carry on moving. Child restraints are designed to protect your child by holding them in place, absorbing some of the forces of the crash and actively controlling how their body moves in order to reduce injury.

When ISOfix seats are compared to properly installed seatbelted car seats, crash testing shows negligible differences between the two. In fact, some seatbelted car seats have out-performed ISOfix seats in tests and vice versa.

Both types of car seat are designed to keep your child safe and ISOfix, as a category, does not offer any statistical safety benefit when compared to a correctly installed belted seat.

And that is the key. A car seat with excellent safety ratings that is incorrectly installed can be fatally dangerous, and belted seats are notoriously complicated and difficult to install.

A which.co.uk investigation in the UK found that 90% of the stores asked to fit two common child car seats made mistakes; some of them serious errors. According to Maxi Cosi, 8 out of 10 parents install their child’s belted car seat incorrectly. Further adding to the problem is that many belted car seats do not have any indicators to warn parents if the car seat is incorrectly installed.

This is where ISOfix seats come into their own and offer huge safety benefits over belted seats. ISOfix was designed to make car seat installation simple and eventually uniform across vehicles and car seats. The risk of incorrectly installing an isofix seat is very low. In fact, their study indicated that 94% of parents use their ISOfix car seats correctly. Most ISOfix units also have indicators to show when the seat is correctly fitted.

The verdict? Belted seats and ISOfix seats offer much the same structural safety. However, ISOfix car seats offer a far more reliable installation. An incorrectly installed is not a safe seat.

WHAT IS The Third Anchorage Point in a Isofix SysteM?

In an accident, a child seat can pivot on it’s ISOfix arms, as it moves forward. This is extremely dangerous! To stop this from happening and to keep the seat from moving forward from the force of a crash, ISOfix seats come with a third anchorage point. This comes in the form of a support leg or a top tether strap.


Photo credit: CSFTL


The top tether strap is a strong fabric strap that come from the top of a child car seat and has a hook on the end. The hook must be connected to a bracket (called a top tether anchor), usually at the back of the rear vehicle seat.

Top Teher Anchor Positions

Photo credit: The Car Seat Lady

The top tether should always be used when it is supplied as part of your car seat's installation system. Before buying a car seat with a top tether strap, please check that the car you are using has the top tether anchor, as this is not a standard in every car.

What is a car seat support leg?

Another third anchorage point used to keep your child safely in position in their car seat is the support leg. The support leg braces the car seat against the vehicle's floor. The support leg extends from the base of the car seat to the floor of the vehicle.

What is a car seat load_leg

It prevents the car seat tipping over or moving forward in a crash and is usually easier to properly install than a top tether. Most of the car seats with a support leg have red and green indicators which show you if the support leg is correctly or incorrectly installed.

Support legs can only be used where the car floor is solid and does not have under floor storage compartments. Please make sure that your car is suitable for a car seat with a support leg before buying one.

Do all new cars come with isofix?

Not all cars are fitted with ISOfix points. ISOfix is more common in newer vehicle models. This is because ISOfix has been introduced at different times in different parts of the world.  Most European cars from 2001 have Isofix. Most of the rest of the world started using the system in 2007 and in Australia ISOFIX only became a standard in 2015. Each car should be checked for ISOfix compatibility before purchasing an ISOfix seat.

Does my Car have Isofix?

The best way to be sure is to check your vehicle's back and front seats yourself. Many cars now indicate the presence of ISOfix brackets with a small round indicator.

Does my Car have Isofix

If you do not have these indicators on your back seats it does not necessarily mean you do not have ISOfix brackets.

To check manually, run your hand between the join in the seat and feel for a u-shaped brackets. There should be two of these u-shaped brackets where one car seat would be installed.

Does my Car have Isofix

Another method to find out if your car is ISOfix compatible is to consult your vehicle’s manual or to check the child seat manufacturer's website for their car fitting list. However, many of the models sold in South Africa have different specs to the same models sold in other countries.

Can you put AN Isofix CAR SEAT on the front seat?

Some cars do come with ISOfix points on the front passenger seat but they are more commonly located on the backseats. This is because it is safer for children to travel in the backseat away from airbags and dashboards.

If your car seat is a rear facing infant seat, you cannot use it on the front seat if there with an active passenger airbag. The force and angle an airbag exerts on a rear facing car seat in a crash, can cause severe injury and even death to the child in the seat.

If your car does have isofix brackets and if you must place your child in the front seat, make sure that the passenger seat is rolled back as far away from the dashboard as possible. This keeps your child away from the dashboard and can help reduce the harmful impacts that can be caused by the release of an airbag.

important Safety note

Never put a rear-facing baby seat in the front if there is an active passenger airbag. It has been proven to be extremely dangerous in a crash and is illegal in Europe. Consult your vehicle AND car seat manuals to check if front seat installation is permitted.

Do you use a seatbelt with Isofix car seats?

When dealing with car seats, parents are most concerned about the safety of their child in the seat. Many parents want to add an extra layer of protection and it is easy to see why they might decide to use both the seat belt and the ISOfixsystem.

Although it might seem logical that two installation methods holding your car seat in place is safer than one, this is not correct in the majority of cases. There is no evidence from the studies done that indicate any benefit from using both ISOfix and the seat belt simultaneously. There are, however, significant dangers.

Car seats are designed and tested to handle the dynamics and physics of a crash in a specific way. It is always best to consult your manual  and to install your seat exactly as it describes. When you install your car seat in a way that is not set out in the car seat manual you are effectively using your child as the crash test dummy.

Manufacturers would only allow the use of both systems if the seat has been crash tested in this way and if the seat passed in this configuration. The Joie Bold is the only exception I am aware of, which must be installed with 3-point seatbelt, ISOfix and top tether anchor simultaneously.

Concerns around using both the car seat belt and the ISOFIX system include:

  • Two installation methods could put additional stress on and break your car seat's body in a crash. 
  • Using both systems at once could change the way the seat is designed to absorb the forces of a crash 
  • Using both systems could mask an improper installation by altering how the seat is positioned or    leaving the installation too loose causing your initial installation to be unsafe. 
Although most ISOFIX systems are not designed to be used with a seat belt there are some seats that have been designed and tested to use both. In all cases it is safest to follow your manual.

Is Isofix mandatory?

In South Africa ISOfix is not mandatory. The main advantage of ISOFIX seats is that they are easy to install correctly. They do not offer significantly better results than a properly installed belted seat and both are legally acceptable in South Africa.

Are all isofix bases the same?

Most infant ISOfix car seats come with a separate ISOfix base that installs firmly onto the car and does not move when you move your car seat. Most toddler ISOfix car seats have integrated bases. Bases can only be used with the car seat of the same brand that it is stated to be compatible with in the manual. 

Not all ISOfix bases are the same. Some connect with a Top Tether, some with a support leg and some with no third point at all. There are 3 distinct kinds of ISOfix bases; Universal, Semi-Universal and Vehicle specific.


Universal ISOfix Car Seats

Universal ISOfix car seats have three anchor points: The two standard Isofix latches as well as an additional top tether anchorage strap that clips behind the seat and  stops the seat from moving forwards or twisting in a crash.Most new cars are created with these three anchorage points but always check your that your manual states that your car is Univeral ISOfix approved before purchasing.

Semi Universal ISOfix Car Seats

Semi Universal car seats are required to have the standard two Isofix latches in the back and a third anchorage point that is not a top tether but usually a support leg. The support leg effectively does the same job as the top tether by stopping the car seat from moving forward or rotating in an accident. Again, it is important to check you vehicle manual to find out is your car is suitable for a semi-universal ISOfix car seat.

Vehicle-Specific ISOFIX Car Seats

These car seats are only tested in car-specific dynamic crash tests and may include special features and designs compatible only for a specific car type. Vehicle specific car seats are not made for use in any other vehicle and are safe to be used only in vehicles named by the car seat manufacturer.

What are iSize Seats?

The latest car seat regulations ECE R129 are a new set of regulations that will ultimately replace the current ECE R44.04 car seat regulations completely and become the only legal child car seats on the market. At this stage there is  no set date when the ECE R44.04 regulation will be phased out.

What are iSize Car Seats

Isize car seats are designed to meet these new ECE R129 requirements:

  • I-size makes rear facing mandatory to 15 months rather than the current 9 Months
  • I-Size aims to addresses the compatibility issues  between ISOfix car seats and the huge range of vehicle models on the market. I-size car seats will ultimately eventually be automatically compatible with ISOfix vehicles.
  • I-size restraints are selected by your child's height and each seat will have an individual maximum child weight limit.
  • The current ECE R44.04 regulations do not require a side impact test. This will be a requirement with i-Size seats.
  • I-size child seats must be installed with the ISOfix mounting making the seat easier to install properly.
  • The internal dimensions of an i-Size seat will be specified and these dimensions will relate to the latest size data for European children.

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