What is i-Size?

i-Size is a new European-wide car seat regulation (the first phase of a safety standard called R129), which aims to make car seats safer.


It’s designed to keep children rear-facing for longer, provide better side impact protection and make car seats easier to fit correctly.

If my car seat isn't i-Size, do I need to buy a new i-Size seat?

No - at least not for several years. The first thing you need to know is that this new i-Size law doesn’t replace the current R44/04 law – the two simply run alongside each other.

The second thing is that the complete R129 law is still being developed by safety experts, law makers, car seat manufacturers and car makers. There will be additional legislation added over the next few years.

So you can still use your current car seats and manufacturers can still sell non i-Size seats until at least 2018, as long as they meet the old regulations.

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So what are the new i-Size changes?

1. Children will be rear-facing for longer

i-Size requires children to sit rear-facing until they’re at least 15 months old. This is longer than the earlier regulations, which advise children to sit rear-facing until they weigh 9kg.

Some new i-Size car seats will enable your child to sit rear-facing up to the age of 4 years, if you wish.

Why? Because studies show it’s safer. Swedish research found that rear-facing car seats can offer up to 75% more protection if your young child is involved in a car accident.

Up to the age of 15 months, your child’s neck is not yet developed enough to withstand the forces of an average head-on collision. The excessive pressure on the neck of your baby might lead to serious neck injury. Rearward-facing seats can help to spread the forces of a head-on collision over a greater area of your child’s body, leading to less pressure on your child's head and neck.

2. Regulated side impact protection

Under the older regulations, car seats only have to be tested for protection against accidents where the front or back of the car is hit. They don’t have to offer side impact protection (although many do), even though around 25% of car accidents involve a car being hit on the side.

i-Size now legally requires car seats to ensure side impact protection.

3. Car seat suitability will be done by height rather than age or weight

i-Size aims to reduce the confusion around car seat suitability. Currently they're categorised by weight - but we often don't know the weight of our toddler or child. However, we do know their age, and so we end up matching weight with age. However, one 9-month-old baby may have a very different weight to another.

i-Size is now being categorised by height. So the best thing to do is to measure your child's height regularly – although the likelihood is, we’ll be matching height with age.

The one age categorisation in i-Size that is important is 15 months. i-Size requires children to be in a rear-facing seat until they're at least 15 months old. Some i-Size car seats will enable a child to sit rear facing until they’re 4 years old.

4. i-Size requires ISOFIX fitting

i-Size currently requires the use of ISOFIX (with support leg or top tether only) to fit your car seat – not seat belts.

Why? ISOFIX can reduce the risk of incorrectly installing your seat. This is the biggest safety problem around car seat use – as evidence suggests that up to 75% of car seats are not fitted correctly.

According to car seat manufacturer Maxi-Cosi, safety tests found 94% of parents use ISOFIX correctly, while only 20% parents install car seats correctly when using a seat belt. Which is a sobering statistic.

5. New child test dummies have been used

A new type of more innovative crash test dummy is being used to test i-Size car seats (they’re called Q rather than P dummies). The new version has more sensors, higher sensitivity and better reflects how a child’s body would react in an accident.

Your i-Size questions answered...

How do I know if a car seat is i-Size?

Firstly, they have this logo (pictured above).

It is similar to the ISOFIX logo, but it has an i on the side. Many of the car seat models also have the letter i in their name or include the word i-Size. And of course, your car seat retailer will be able to confirm this for you.

Do i-Size car seats fit any car?

No. This is an important point. It’s not enough that your car has ISOFIX fittings, this doesn’t mean the seat will fit safely. Currently you need to check that your car model is on the fitting list for the i-Size car seat you want.

Here are some of the main car seat manufacturer fitting lists

Are there i-Size car seats for older children – eg Group 2/3?

Currently no. i-Size only covers car seats for children up to 105cm tall (around 4 years). However, car seats for older children are likely to form part of a later phase of the new regulations.

Can you get ISOFIX fitted to a non-ISOFIX car?

Cars manufactured from 2011 come with ISOFIX as standard. However, if your car is older than that you may be able to buy an ISOFIX conversion kit. The kit costs around £17 each and can be fitted in one hour for about £90. But it’s worth noting that the older a car is, the less likely it will be compatible with the kit. And any cars made before 1997 won’t be able to accommodate any i-Size car seat.

When will parents have to stop using old car seats that face forward at 9 months?

The two laws will run side-by-side until at least 2018. When the law changes to only allow iSize seats to be sold, parents won’t be able to buy any old-style seats from new.

But parents will still be allowed to use their existing seats for some time (probably a few years) afterwards.

And will there be a time when only ISOFIX car seats are sold?

It’s a similar story as above. “i-Size seats are designed to be fitted into the ISOFIX points in cars," explains Kevin Clinton, Head of Road Safety at the Royal Society for the Prevention of Accidents (RoSPA).. "So when the law does formally change to only allow i-Size car seats to be sold in stores, manufacturers will have to stop producing new car seats that are installed with seat belts.

"However, parents will almost certainly be allowed to continue to use any existing seats they have, even if they are installed with seat belts, for some time afterwards."

So when could this be enforced and police start checking parents’ cars?

"We’re not aware of any enforcement campaigns being planned," says RoSPA’s Kevin. It looks like the emphasis will be on parents ensuring they’re following the latest guidelines on car seats.

So if you have a non-iSize car seat, what should you do?

“RoSPA’s advice to parents, who are using non-iSize [R44] seats, is to keep their child rearward-facing for as long as possible,” explains Kevin.

“Only move them to a forward-facing seat once they can sit up unaided and they have exceeded the maximum weight for the baby seat, or the top of their head is higher than the top of the seat. Or consider using a rear-facing for longer Group 1 seat.”

So, how are car seats likely to change in the future?

New car seats are likely to become more versatile, believes Julie Dagnall, Director of Child Seat Safety at Road Safety UK.

“I suspect we will see car seats that are designed to be more adaptable - either by additional support cushions or moveable sections to extend/reduce/increase the seating capacity of the child,” she explains. “A bit like an adjustable cycle helmet which allows for a snug fit rather than a generic one. But we will just have to wait and see what technology the manufacturers introduce.”


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Hazelann WilliamsFormer Reviews Editor

Having been a journalist for 15 years – and Reviews Editor at MadeForMums for five of those – Hazelann has accrued a lot of experience testing and reviewing every baby product imaginable.