Skip to Content

Diono Rainier Convertible Plus Booster Car Seat Review

diono rainier car seat review

Disclosures: I was provided the Diono Rainier Covertible + Booster car seat for review at no cost. All opinions are my own.

From the moment you hold your newborn baby in your arms, you want nothing more than to protect them from anything and everything bad in the world. Motor vehicle accidents are the #1 cause of unintentional deaths for children ages 0-19 in the United States, according to statistics gathered in 2007. While I consider myself and my husband to be pretty safe drivers, you never know what can happen on the road, and there are plenty of other drivers out there that I don’t trust! That’s why deciding on the car seat our children will ride in is of the utmost importance to us. Over the years, I have spent many hours researching the best car seats!

Ever since our family had the opportunity to review the Diono Radian RXT, my husband and I have been huge fans of the Diono brand.  So, when I was offered the opportunity to review one of their newest convertible car seats, the Rainier Convertible Plus Booster, I eagerly agreed!

Diono burst into the child car seat world in 1999 when they introduced the Mighty Tite, a device designed to assist parents in tightening the seat belt during car seat installation. They then released their first car seat, the Radian, in 2005, which was the first ever steel-reinforced folding car seat, designed to make travel and storage more convenient than ever. Today, Diono continues to produce innovative car seats, convertible boosters, storage solutions, stroller and travel accessories and other pieces of baby gear that consistently earn high ratings from industry experts and families worldwide.

The Rainier is taking Diono car seats to a whole new level thanks to their new, extra deep side walls, providing enhanced side impact protection. The aluminum reinforced headrest has 12 height positions for adjustable head support and additional EPS foam surrounds the child’s head and body for complete side impact protection. The Rainier is also NCAP crash tested, the industry benchmark for verifying child seat performance in severe accident conditions.

Diono Rainier Car Seat Review

Research has shown that children are safer in the event of a crash when their car seats are rear-facing and the Diono Rainier gives you extended rear-facing capabilities. In fact, your child can comfortably rear-face in this car seat from 5 to 50 lbs.!  When you are ready to forward-face the Rainier, it is approved for children weighing 20 to 90 lbs. in 5-point harness mode (up to 57″ in height). As of the date of this publication, this is the highest forward-facing capacity of any car seat with a 5-point harness. Additionally, it converts to a booster for children between 50 and 120 lbs. or up to 57″ in height.

This seat comes with a body support pillow (to be used for infants and toddlers) and a head support pillow (to be used for infants). As I’m typing this review, our new baby hasn’t arrived yet, but if we chose to use it for him/her, we could. To be honest, I prefer an infant car seat for the first few months because of the convenience of being able to take the infant car seat in and out of the car with ease. However, it is important to note that you CAN use this seat with your newborn (as long as he/she is at least 5 pounds). If you are on a budget, purchasing this seat to begin using at birth will save you money in the long run, since it would probably be the only car seat your child would ever need thanks to its industry-leading 12 year product life (from the date of purchase).

Diono Rainier Car Seat Review

Now that you know the basics of this seat, let’s talk about securing it in your vehicle. I can NOT stress enough how important it is to read the manual that comes with this car seat (or any other car seat you are using for that matter!). Every car seat is different and in order to achieve the safest installation, it’s important to read the directions and follow them. I have already flipped through the manual a dozen times for this seat. Like other car seats on the market these days, you have the option to install using LATCH or the seat belt depending on your vehicle.

The manual gives clear, easy to follow instructions to install using the method of your choice. My son is 26 pounds right now and turned 2 in May. We practice extended rear-facing, so we installed the Rainier rear-facing using the LATCH system. As you can see in the pictures below, we also used a Diono angle adjuster to put his seat at a more upright angle and leave more room for the front passenger seat. It’s important to note that you can not use the angle adjuster for newborns or infants.

Here is what it looks like for my son ( 25 months and 26 pounds) and my daughter (age 4 and 32 pounds) to rear face in the Rainier. My son will be the one using this seat (Maggie already has her Radian RXT) but I wanted you to be able to see how it looks for their size/weight.  They are both quite comfy and have plenty of room for growth.

Diono Rainier Car Seat Review

When you purchase your Rainier, it will arrive with a number of extra pieces and accessories. Included (and pictured below) are:

  • Additional set of harness pads to use only when the child is over 65 lbs in the 5-point harness
  • Angled cup holder
  • Head and body support pillows (as mentioned and shown above)
  • Detachable base (only used for rear facing)
  • Top tether strap for rear-facing installation

Diono Rainier Car Seat Review

The Rainier is approved by the FAA for airplane travel. It folds flat for easy storage and transport. If you plan to fly often with your Rainier, you can purchase a carry strap for your shoulder, or 2 carry straps to wear it like a backpack. You can also carry it by the red security strap, as my husband is demonstrating below.

Diono Rainier Car Seat Review

Radian RXT or Rainier?

If you are debating between the Radian RXT and the Rainier, you are probably wondering what the differences are.  The main difference comes down to the weight of your child and the longevity of each seat position and the car seat itself. The new Rainier can be used in the rear facing position from 5-50 pounds, while the Radian RXT can only be used for 5-45 pounds. At the rate my children gain weight, the extra five pound weight limit would probably give them an additional 6 months to a year of rear facing time. Once you decided to forward face your child, the Rainier can be used from 20-90 pounds with the 5-point harness, while the Radian RXT can only be used for children 20-80 pounds. Again, this is giving your child an additional 10 pounds of growth before they need to change to a booster.

The Rainier has a product life of 12 years, while the Radian RXT has a 10 year life.

The Radian RXT is also trimmer and gives you the ability to fit 3 across a row, while the Rainier is a little bit wider and therefore you’d probably have trouble using it if trying to fit 3 across (I actually tried it with 2 Radian RXT seats and this Rainier in my Honda Odyssey and it would not fit).

There are 2 other differences I noticed between the Radian RXT and the Rainier: price (The Rainier is priced higher and sale prices are not as discounted right now) and available colors/prints.

Are they any things about the Rainier I would change? Yes, two things. When it is time to adjust the straps, you will need to rethread them. With many car seat manufactures switching to a norethread system, I hope that Diono will also do the same soon. This is certainly not a deal breaker for me, but one worth mentioning. I also wish it was trimmer, like the Radian RXT so that we could fit three across a row.

My son seems extremely comfortable riding in his seat, and the lower sides mean that he is able to climb in on his own now, without my husband or I having to assist him. Since I’ll be recovering from childbirth over the next few weeks, this makes me extra happy! I feel like my children are as safe as they possibly can be when they are riding in their Diono seats, and I love knowing that my son can use this seat for years to come. Overall, we are once again quite pleased with this car seat from Diono!

The Diono Rainier has a suggested price of $359.99. You can purchase it through (my favorite) or use the Diono store locator to find a location near you. You may also be interested in reading my Diono Pacifica Convertible + Booster Car Seat Review.

Disclosures: I received the car seat mentioned above at no cost to facilitate this review. All opinions are my own and may differ from yours and/or Diono’s. Amazon links are affiliate links.


Thursday 23rd of July 2015

I just purchases a Diono and I am extremely excited to start using it! The additional heat rest says it is for infants, when do you stop using that? Also, the body pillow says it is for infants and toddlers in the read facing position. Again, when do you stop using that? My son is 20 lbs and 10 mo. old. I hope to have him rear facing as long as possible.


Thursday 23rd of July 2015

Hi Whitney, Congratulations on your new Diono! Which model do you have? Is it the Rainer or one of their other ones? Usually you'll want to use the infant body pillow until your son doesn't need it for the support anymore. I'd say at that size, he probably doesn't need it, but if you feel like he's more comfortable with it, then you can keep it in there until he's too squished. Same with the head rest -- use it if he seems like he needs it, but rear facing he should be reclined enough that he's probably old enough and big enough that it's not necessary.


Friday 5th of December 2014

Great review! We purchased the Rainier and are quite happy with it so far. Our only issue is that we find it hard to tighten the harness straps when the seat is rear facing. Any suggestions? Thanks again for your post.

Lily Kwan

Thursday 10th of July 2014

This car seat looks very nice. Thanks for sharing!

Katie Hubbard

Thursday 10th of July 2014

After browsing Diono's site, I'd like the Cozy Coupe Harness Packpack. It'd be great on trips!

Katie Hubbard

Wednesday 9th of July 2014

I love the weight limits on this seat!