Founded in 1999, Diono is an American company that manufactures travel solutions for families. The Radian 5 is one of Diono’s core products and is described as “the original three-across car seat”, referencing the fact that it’s only 45cm wide, so you could fit three of them across the back of most cars.
On the face of it, the Radian 5 has a lot to offer. This group 0+, 1 and 2 car seat can be used rear-facing from birth until your child weighs 25kg (when they’re around the age of six) and you can use it in the forward-facing position too; that’s suitable for children that weigh between 9 and 25kg.
Despite being relatively slimline, safety isn’t compromised. The Radian 5 seat has a full steel frame, it has a foam protective lining and a five-point safety harness. However, it isn’t ISOFIX compatible, which can make fitting it into your car tricky.
Comparatively, the Britax Multi Tech II car seat can also be used in both the rear and forward-facing position until your child is around six years of age. This car seat isn’t ISOFIX compatible either and it comes in at £250. However, unlike the Radian 5, it isn’t suitable from birth – your child needs to weigh at least 9kg to be able to use the seat.
The Radian 5 could also be compared to the Jané Gravity i-Size, which is another product that prides itself on its safety credentials. This seat can be used from birth until your child is around four years old and it has the advantage of using an ISOFIX point. However, with an RRP of £349.95, it is more expensive and it can’t be used for as long.
I was quite overwhelmed when I first saw the Radian 5. It seemed to have lots of parts to it and it didn’t look simple to construct or to fit into the car. After looking at the instructions, I decided that this wasn’t an item I could fit alone, so I asked my partner, who is an engineer, to help me. I’m not particularly practically minded and the seat looked too complicated for me to fit correctly.
I thought that it felt very solid though and I was impressed by the seat padding, as it looked comfortable.
What age is the Diono Radian 5 designed for – and what age did you try it with?
Themulti-stage seat is designed to be used from birth until your child is around six years of age. I tested the seat with my four-month-old son.
The seat has extended rear-facing capacity from birth to 25kg (112cm tall).
How comfy do you think it would be for a child at this maximum weight limit to use rear-facing?
The Radian 5 seems very robust and the padding looks and feels soft to touch. I think that a child at the maximum weight limit would be comfortable using the seat.
In what different modes can you use the Diono Radian 5?
You can use the seat in a rear-facing position from birth until your child weighs 25kg. You can flip it to a forward-facing position once your child weighs 9kg.
How easy is it to install?
We installed the seat in a rear-facing position. The seat was quite complicated to build and fit and we had to watch a YouTube video to work out how to attach the front tether. In total, it took about an hour to build and fit the car seat.
Does it feel secure once in place?
It feels very secure and once installed you couldn’t easily move it out of position.
How did you like the harness on the Diono Radian 5?
The harness was quite tricky to fasten, but once strapped in, my little boy felt secure. The padding on the harness also makes it feel comfortable.
How easy is it to swap between different age users (removing harness, adjusting headrest etc)?
The adjustment is similar to harnesses on other seats and prams. However, the access at the rear is a little tricky and it’s complicated by the weight of the product. Use of the instruction manual is essential.
What do you think of the design?
I was impressed. The seat looks very comfortable and a cup holder can be added when your child gets a bit older.
Does it feel sturdy?
It does feel sturdy and my son seemed very secure when he was strapped in.
Are there different seat positions on the Diono Radian 5? Does it recline?
There are two different seat positions, forward- and rear-facing. An attachment is used for the rear-facing position to recline the seat. The headrest height is adjustable, but even at its lowest setting was still higher than our baby’s head.
How comfortable is it for your child?
The seat wasn’t that comfortable for my son. It was ok when he was first strapped in, but when he fell asleep his head tended to flop which didn’t look comfortable at all. Also, despite not being a refluxy baby, he did tend to bring up more milk than usual while sat in the seat.
Tell us about its main safety features?
The seat is made of steel with aluminium-reinforced sidewalls and it’s clear from the weight of the seat that there’s a lot of metal in it.
In the forward-facing position there’s a safe-stop shock absorber to reduce the force of a crash and it’s one of the few seats to have a top tether in the rear-facing position. For children over 25kg there are supergrip harness pads which protect the child’s neck in the event of a collision.
What do you think of the size of the Diono Radian 5? How easy is it to get in and out of the car and swap between cars?
This seat has been designed for safety over convenience. Its large and heavy, which is fine for long-term use in one car, but I wouldn’t recommend it for parents who would be regularly switching it between cars.
Is it easy to clean?
The seat is easy to clean. I used baby wipes and muslin cloths to wipe away baby sick and dribble from the seat. The cover can also be fully removed and washed in the machine. I think it’s great that you can wash the cover – this gives me high hopes that the seat would last the distance.
How heavy is the Diono Radian 5? Would you take it traveling with you?
The seat weighs 11kg, so it’s pretty heavy. But it does fold down neatly and you can buy a travel bag to put it into. The seat can also be used in the forward-facing position on aircrafts by children that weigh between 9kg and 25kg. However, the Radian 5 proved tricky to install in my own car, so I think I’d find it stressful using it on a plane or in a hire car. For that reason, I wouldn’t personally travel abroad with it and I’d only use it in my own car.
What feature do you like best in the car seat?
I think it’s great that the car seat is only 45cm wide. This means that we could potentially fit three seats in the back of the car – you can’t do that with many brands.
What does the Diono Radian 5 cost, and does it deserve the price tag?
It costs between £230 and £290, depending on what colour you choose. I think it does deserve the price tag, as you could potentially use it over a six-year period.
How easy was the car seat to assemble? Were the instructions useful?
The seat was quite tricky to assemble. The instructions were ok but for certain aspects, such as the top-tether, we had to look at Diono’s official YouTube videos for additional assistance. We found these videos clear and informative.
Who is the Diono Radian 5 car seat best for?
The seat is best for children aged between 18 months and six years.
What do you wish you had known before you got it?
The limitations of using this seat with a baby. You can’t easily take the seat out of the car if your baby is sleeping, head flop is an issue and it’s not travel system or ISOFIX compatible.
Would you recommend this car seat?
I wouldn’t recommend this car seat for babies. But it is a good quality product and I think I will get a lot of use out of it when my son is a little older.
What’s in the box?
The Radian 5 car seat, harness pads, a cup holder, a tether strap, a safe-stop strap, a rear-facing angle adjuster, an infant padded cocoon, a rear-facing back pad and an instruction manual in various languages.
Are there any accessories required or available?
The seat comes with one cup holder and you can buy others. I’d say that a car mirror is an essential purchase, especially if you decide to use this seat with a baby. The Diono Easy View Plus mirror costs £20, but you could pick up a cheaper alternative online. For an additional £50, you could also purchase a bag for the Radian 5, which would be handy if you decided to travel with it.
This car seat does feel sturdy and robust, however, I don’t think it’s suitable for a 4-month-old child. I was concerned when my son fell asleep in the seat as his head went floppy. I also found that he vomited more than usual while sat in the seat; I think this was down to the positioning. Another disadvantage is that I couldn’t carry my son out of the car in the seat when he fell asleep and it isn’t travel system-compatible.
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Child age (approx)
Birth to 6 years – approx up to 6 years old
Up to 25kg
Dimensions & Weight
Car seat installation
Travel system compatible
Positions of carry handle
Removeable cover for washing
Side crash protection
Height adjustible headrest
Suitable from birth with extended rear facing capacity to 25kg
Forward-facing with 5-point harness from 9kg up to 25kg
Full steel alloy frame for head to hip protection
Side impact protection
Energy absorbing harness pads
Expandable sides and extendable headrest
Folds flat with carry straps for easy transportation