Cybex Sirona Gi i-Size review: our verdict on the new 360 extended rear-facing car seat

RRP: £300-£325 | Buy now from Amazon

Key specs

Age range: From birth with newborn inlay; otherwise from 3 months to 4 years (or 20kg); 61 to 105cm (from 40cm with newborn inlay) | Safety credentials: i-Size (R129), integrated Linear Side-impact Protection (LSP), energy reduction technology for safer forward-facing, travel rear-facing for longer | Fixing system: ISOFIX | Dimensions: 71 x 44 x 75cm | Weight: 13kg | Warranty: 3 years

What we like

• 360-degree rotation for easy boarding

• Integrated air ventilation and mesh fabrics

• Easy recline with five different settings

• Fast one-click installation with indicators to ensure correct fitting

• Padded seat

• Good value for money

What we don’t like

• 360-degree rotation mechanism sometimes quite stiff

• Limits how much the adult seat in front can move or recline

• Unsuitable for babies under 3 months unless newborn insert bought separately

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Our verdict on the Cybex Sirona Gi i-Size

• Installation: 4.5/5

• Safety: 5/5*

• Ease of use: 4/5 

• Design: 4.5/5

• Ease of cleaning: 4/5

• Value for money: 4.5/5

*Safety rating reflects standards, safety features and independent crash-test evidence where available. Mumsnet does not carry out crash testing.

With excellent safety credentials, high-quality fabrics and an integrated ISOFIX base, the Cybex Sirona Gi i-Size car seat is worth investing in.

Suitable from birth with the newborn insert or from three months old without, this extended rear-facing car seat will last until your child is around four years old or 105cm in height, whichever comes first.

You can switch to forward-facing with this car seat from 15 months (or 76cm), but I like that the Sirona Gi i-Size can be used rear-facing all the way up to four years old, which is the safest way for infants and toddlers to travel. 

While I think the 360-degree feature is a game-changer for parents, the mechanism can be quite stiff, which is the only thing that lets the Cybex Sirona Gi i-Size down. I have the similarly designed Joie i-Spin 360 as my main toddler car seat and it just pips the Sirona Gi to the post in this regard. 

How we tested the Cybex Sirona Gi i-Size

• Three months of using the Cybex Sirona Gi i-Size multiple times a week

• Used on both short and long car journeys

• Tested with a 18-month-old toddler

I tested the Cybex Sirona Gi i-Size car seat out with my now 18-month-old toddler. We used it at least three times a week during the 15-minute nursery run and for running short daily errands as well as on longer car journeys of 40 minutes or more. This was to see how comfortable the seat was over a longer duration.

As part of the testing process, I scored the car seat out of five in a number of different categories including: installation, safety and stability, ease of use, comfort, design, ease of cleaning and value for money.   

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Cybex Sirona Gi i-Size: what’s in the box?

• Cybex Sirona Gi i-Size toddler car seat

• Integrated ISOFIX base

• User guide

While not included, the Cybex Sirona Gi i-Size is also compatible with the Cybex Car Seat Cup Holder, Cybex Sirona Gi i-Size Newborn Inlay and the Cybex SensorSafe 4-in-1 Kit, which acts as a temperature sensor and harness monitor among other things.

How easy is the Cybex Sirona Gi i-Size to install?

Installing the Cybex Sirona Gi i-Size is relatively easy. It has simple visual instructions stuck to the side of the seat so that you have them to hand at all times. There’s also a more detailed user guide included in the box. 

It took me 15 minutes to fully install the Sirona Gi i-Size as I initially had some trouble connecting the car seat base to the ISOFIX points in my Ford Fiesta. However, this was more an issue with the anchor points in my car than the car seat itself. 

I like that the Sirona Gi i-Size has helpful green and red installation indicators both on the base and the load leg. This reduces any margin for error, even if you’re in a rush, and offers reassurance that the car seat has been installed correctly. 

To install the car seat, you simply connect the integrated base to your car’s ISOFIX points before extending the load leg to the right height. The indicators will then turn green when both elements are correctly installed. 

Read next: The best car seats for 4-year-olds and beyond

Cybex Sirona Gi i-Size: how does it look?

The Cybex Sirona Gi i-Size is a car seat that will appeal to most families. The regular Gi i-Size comes in either Moon Black or Lava Grey, and has some small but aesthetically pleasing details on the cover.

I tested out the Plus version, which boasts additional mesh in the seat for added breathability. At £325 (versus £300 for the original), it’s slightly pricier than the normal Gi i-Size, but comes in three additional colourways: Ocean Blue, Beach Blue and Hibiscus Red. 

Mine was in Moon Black and I liked both the colour and design. For some contrast, it has white detailing on the edges of the harness pads as well as down the centre of the seat, which I thought was a nice touch. 

One of my favourite things about the Sirona Gi i-Size Plus is just how plush and padded the seat cover is. It feels lovely to the touch and ensured optimal comfort for my toddler on all car journeys.

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Is the Cybex Gi i-Size safe?

The Cybex Sirona Gi i-Size meets the R129 (i-Size) European car seat regulation, which sets the legal safety requirements for child car seats sold in Europe. R129 introduced changes designed to improve child protection compared with older standards, including mandatory side-impact testing and the use of more advanced crash-test dummies.

Under R129, car seats are classified by a child’s height rather than weight, and must pass both frontal and side-impact crash tests. The car seat regulation also requires children to travel rear-facing until at least 15 months of age.

One feature of the Sirona Gi i-Size is that it allows children to remain rear-facing until four years old or 105cm. Car seat safety experts consistently recommend rear-facing travel for as long as possible, as it offers better protection for a child’s head, neck and spine in a collision.

The Cybex Sirona Gi i-Size seat includes Cybex’s Linear Side-impact Protection (LSP) system, which is designed to help reduce crash forces in the event of a side-impact collision. Cybex also uses its own energy-reduction technology, intended to manage forces during forward-facing travel if parents choose to turn the seat once their child meets the minimum age and height requirements.

Because it's a relatively new model, the Sirona Gi i-Size has not yet been independently crash-tested by organisations such as ADAC, which publish comparative safety scores for car seats. Cybex says it has carried out internal testing using the 2022 ADAC frontal crash-test criteria, but this is not a substitute for independently published results.

In everyday use, the Sirona Gi i-Size feels sturdy once installed, and the five-point harness is straightforward to buckle and tighten using the pull-strap. Once adjusted, the harness stays securely positioned during normal use, helped by grip strips on the underside of the shoulder pads designed to reduce slippage on clothing.

Unlike some rotating seats, such as the Joie i-Spin 360, the Sirona Gi i-Size does not include a mechanism to physically prevent the seat being turned forward-facing before 15 months. Instead, a clear safety label on the top of the seat acts as a visual reminder of the rear-facing recommendation.

What's the Cybex Sirona Gi i-Size like to use day-to-day?

I was really impressed with how easy the Cybex Sirona Gi i-Size slotted into my family’s daily routine. The harness straps can be pinned to the side of the car seat once your child is out of the seat so that you can easily get your toddler in the seat for the next car journey. The pull-strap mechanism also ensures you can loosen and tighten the strap for easy in and out, even in a hurry. 

Less bulky than the Joie i-Spin 360, which I use daily with my toddler, the Cybex Sirona Gi i-Size fits well in the back of my small Ford Fiesta, although there is a limit to how much you can recline or move the front passenger or driver's seats. As my husband is 6’4”, this can prove an issue on longer car journeys. At 13kg, it’s also not a car seat you’d want to switch between cars regularly and, because of its ISOFIX base, you also won’t be able to use it on a plane. 

If you have twins or two under four, you’ll find it tricky to have two 360 spin car seats in the backseat at any one time. I tested this out by installing my Joie i-Spin 360 alongside the Sirona Gi i-Size and found that both car seats couldn’t be spun at the same time as there wasn’t enough room. This might have been different if I had a larger car. 

Despite this, the Sirona Gi i-Size is a car seat that’s been very well designed. By far its most useful feature is the 360-degree rotation, which, in my opinion, is a must for getting toddlers in and out of their car seat. With that said, the 360 mechanism is stiffer than that on the Joie i-Spin 360, and is the only real frustration I have with this seat. 

Because it’s an extended rear-facing seat, I find it reassuring to attach a car seat mirror to the headrest of the back seat so that my daughter is in view at all times. 

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How comfortable is the Cybex Sirona Gi i-Size?

As toddler car seats go, the Cybex Sirona Gi i-Size is one of the most comfortable I’ve tested. If you regularly travel long distances by car, you’ll likely want to upgrade to the Plus version because of the mesh fabric and all-round air ventilation system which offer greater breathability and help to keep your child cool, particularly during the warmer months. According to Cybex, the mesh “increases breathability up to six times compared to regular fabrics.”

My 18-month-old daughter enjoyed sitting in the car seat on both short and long journeys, especially as it’s similar in style to her usual car seat, the Joie i-Spin 360. However the Sirona Gi i-Size feels more comfortable for her to sit in thanks to the padding and mesh.

The seat can be adjusted easily to fit different heights as she grows by using a button at the back of the headrest, with 12 different settings to choose from. There are also five recline positions to choose from depending on preference, with a recline mechanism that’s smooth to operate.

While I wasn’t able to test how this car seat fared with a child at the top end of the age range (age four), I do feel there is enough leg room to keep my toddler comfortably rear-facing for as long as the car seat allows. 

What’s the Cybex Sirona Gi i-Size like to use with a newborn?

While I didn’t personally test the Cybex Sirona Gi i-Size out with a newborn, the beauty of this car seat is that it can be used from birth with the cosy Cybex Sirona Gi car seat inlay (£45). If you don’t want to buy the newborn insert, you won’t be able to use the car seat until your baby is three months old or 61cm in height. 

Read next: Newborn essentials checklist

Is the Cybex Sirona Gi i-Size easy to clean?

Generally, yes. The Cybex Sirona Gi i-Size cover is machine-washable at 30 degrees. It took me some time to figure out how to remove the cover in its entirety, especially as there are a few different elements. I also needed to remind myself how I took the cover off so that it was easier to put back on again after washing. 

I like that the shoulder straps attach to the harness with poppers, which make them easy to remove for cleaning. As my seat is in Moon Black, stains are easily hidden, but for any that aren’t, I found it quicker and simpler to spot-clean the seat rather than remove the cover completely.  

Read next: The best baby carriers, wraps and slings

Does the Cybex Sirona Gi i-Size offer good value for money?

Absolutely! The longevity of the Cybex Sirona Gi i-Size makes the car seat worth the cost, especially as it comes with an integrated base. It also retails at a similar price to many other 360 car seats on the market. 

While it doesn’t come with a newborn inlay as standard, it’s a good idea to buy this if you want to use the Sirona Gi i-Size as soon as your baby is born. 

It’s not essential to upgrade to the Cybex Sirona Gi i-Size Plus if your budget doesn’t allow it, however my toddler found the more breathable seat to be very comfortable, particularly during the summer when my car typically becomes a sweatbox. 

Granted, there are other top-performing 360 spin car seats out there like the Joie i-Spin 360, which retails slightly cheaper than the Sirona Gi i-Size, however I much prefer the seat padding on the latter. 

While the 360-degree mechanism could be smoother, this was still one of my favourite features. That, coupled with the extended rear-facing option and plush fabrics, makes the Sirona Gi i-Size more than worth its price tag in my opinion. 

About the author

Laura Westerman is an editor, writer and Deputy Head of Editorial Content at Mumsnet. Mum to a one-year-old, she’s always keen to make travel safe and fun for her daughter, so is fully invested in discovering the best and most affordable baby products on the market, and sharing her knowledge and findings with other parents.

With over seven years' experience as a full-time editor, five of which have been spent writing, commissioning and editing car seat reviews and round-ups, Laura has a keen eye for what parents love and likes nothing more than putting together honest reviews to make parents' lives that little bit easier. 

In addition to her work as a writer and editor, she has also appeared in a number of baby product videos for Mumsnet's YouTube channel.

About Mumsnet Reviews

All Mumsnet product reviews are written by real parents after weeks of research and testing. We work hard to provide honest and independent advice you can trust. Sometimes, we earn revenue through affiliate (click-to-buy) links in our articles. However, we never allow this to influence our coverage.

Our safety rating looks at whether a car seat meets current legal safety standards (such as R129), the safety-related features it includes (for example rear-facing capability and side-impact protection), and how clearly it supports correct everyday use.

Where independent crash-test results from organisations such as ADAC or the Swedish Plus Test are available, these may also feed into our safety rating.

Our rating is not a crash-test score and doesn’t assess how a seat would perform in a real-world collision. Mumsnet doesn’t carry out crash testing.

Because not every car seat has independent crash-test data, our safety rating shouldn’t be read as a full, like-for-like comparison of crash protection across all models.