Isofix child seats

Improved safety from 'plug in' seats – but check the handbook first

Child restraints with latches on the back to lock onto dedicated attachment points in cars

Child restraints with latches on the back to lock onto dedicated attachment points in cars

The seats and seat belts in your car are designed for the comfort and protection of adult passengers so it's not surprising that it is sometimes difficult to install child seats properly.

Isofix overcomes these problems by providing dedicated attachment points in the car for 'plug-in' child seats.

The concept of Isofix was put forward in the early 1990s though it took more than a decade for the technical standards to be agreed.

The idea is simple. Car makers provide small, cheap and inconspicuous attachment points in standard locations in new cars, and child restraints are designed with latches on the back to lock onto these with a simple push and click

Benefits of Isofix

The aim with Isofix was that it would:

  • be a standard, universal means of attaching child restraints
  • eliminate fitting problems common with the use of adult seat belts
  • improve performance in a crash by connecting the child seat directly and rigidly to the car structure.

These aims have largely been achieved though it has to be said that Isofix is not as easy to understand and as simple to use as hoped. Cars don't all have the same anchorages and the seats aren't all 'universal' so you do still have to do your homework before buying and must check the vehicle handbook.

Forward rotation

The two latches at the back of the child seat stop it moving forwards but the weight of the child and child restraint is supported by the adult seat cushion. If the cushion is too soft - there are no regulations - then the child restraint can rotate forwards in a crash, increasing the forces on the child and the risk of injury.

To control forward rotation a 'universal' Isofix child restraint has to have a third, rigid point of attachment. This may be either a rigid leg between the front of the child restraint and the floor of the car or a 'top-tether' strap connecting the top of the restraint to a dedicated fixing point on the parcel shelf, boot floor or seat back.

An Isofix seat with a support leg may not be compatible with some cars where under-floor storage is provided - the storage cover/floor surface may not be strong enough.  Check the vehicle handbook and child restraint application list carefully.

Two-stage process

Because of delays in agreeing standards and following a compromise between car manufacturers and a European standards working group Isofix anchorages have been introduced into cars in two-stages.

Early cars with Isofix anchorages were fitted with a two-point system only. Because the car seat cushion plays a crucial role in performance these must only be used with Isofix child restraints specifically approved for use in that car. These semi-universal or vehicle specific Isofix seats will have an application list showing the makes and models of car they are approved for.

Later cars have had two or more seating positions provided with 'three-point' Isofix anchorages - two-point plus top-tether. This makes them suitable for ISOFIX child seats in the universal category.

Isofix classes

As well as different categories of Isofix seat, 'universal' and 'semi-universal', there are different size classes too. This is because a full height forward facing restraint may not fit in the back seat of a small car.

Main Isofix size classes

  • A – ISO/F3: full height forward facing toddler child restraint
  • B – ISO/F2: reduced height forward facing toddler child restraint
  • B1 – ISO/F2X: reduced height forward facing toddler child restraint
  • C – ISO/R3: full size, rearward facing toddler child restraint
  • D – ISO/R2: reduced size rearward facing toddler child restraint
  • E – ISO/R1: rearward facing infant child restraint

Check the vehicle handbook

You must check the car handbook before buying an Isofix child restraint to make sure you buy the right category and size class.

For every seating position and child mass group the handbook will give detailed information about the categories (Universal/semi-universal/model specific) and size classes of Isofix child restraint that can be used.

The handbook will also give you clear instructions for attaching a child restraint to the lower and, if fitted, upper anchorage points.

(19 June 2012)