Britax, Cybex

Cybex Eternis S Vs Britax One4Life

Convertible car seats Cybex Eternis S Vs Britax One4Life are perfect for parents who want to use the seat from day one until the kids are in elementary school. They are very convenient, easy to install, and high value because the seats can last for several years. If you wonder which seat will be the better choice, let’s see below what they can offer.

In this comparison, we are going to talk about:

  • Why Safety Car Seat is Necessary
  • What are Cybex Eternis S and Britax One4Life
  • How is the Design of Cybex Eternis S and Britax One4Life
  • How to Install Cybex Eternis S and Britax One4Life
  • How is the Fitting of Cybex Eternis S and Britax One4Life
  • What else Cybex Eternis S and Britax One4Life can offer
  • Cybex Eternis S Vs Britax One4Life

Safety Car Seat for Children 

The road is not the safest place to be, but it is inevitable to be there while traveling with almost any vehicle. As parents, we are always worried about our kid’s safety, and because their body is still small, the seat belt won’t be able to fit and secure them properly. A safety car seat is necessary to help parents secure their kids while in the car or public transportation. Car seats are also mandatory in many countries and states, so it is required to have them.

We need a safety car seat to secure the passenger on their seat when there is an impact. Seat belts are designed for adult bodies, so they are large and won’t be able to secure young children. Anything that is not strapped into the seat will hit the interior, or worse, may get ejected. The physical impact can be dangerous for the passenger and not limited to injury, but it may also cost their life.

Safety car seats replace the role or car seat belt, so the children stay in their seats during the impact. Depending on the model, most car seats use a five-point harness to buckle the passenger on the compartment, and as they get older, the car seat may use a seat belt instead. The latter is a booster seat, and the purpose is to increase body height so parents can position the seat belt properly across the shoulder and hip of the child.

 Cybex Eternis SBritax One4Life
Product Dimensions25.3 x 20 x 25.5 inches
‎20.5 x 19.5 x 25 inches
Shipping Weight26 pounds
30 pounds
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About Cybex Eternis S and Britax One4Life

Safety car seats for children have weight and height limits, making them easy to find and choose. Parents can decide the seat according to the kid’s weight and height or the installation process. It is necessary to install the seat properly because the seat can be secure only when it is firmly attached to the vehicle. Overall most parents only need one or two seats for each kid. The first seat can be an infant car seat or convertible seat, and the last seat is a booster.

A convertible seat is the most convenient and versatile because it can face the rear and front according to the weight and height limit. Some of them, such as Cybex Sirona S Vs Evenflo Revolve, offer an exciting feature where you can rotate the seat when putting in or getting the passenger out. But, if you want something that can stay useful for long, the 4-in-1 seats like Cybex Eternis S and Britax One4Life are some of the best seats to consider.

These two should be useful from day one to at least when the kids are in elementary school. There is no guarantee that our kids can use the seat until a certain age because they grow rapidly. The faster they grow, the faster we need to move into the next seat; in this case, you may need a high back or backless booster seat. Both Cybex Eternis S and Britax One4Lifea are very similar and can offer the same convenience. But, parents may be able to use the One4Life longer.

The main difference between Cybex Eternis S and Britax One4Life is their highest height capacity. The latter seat can fit children up to 63 inches tall and 10 pounds heavier than Eternis S. We also prefer the installation method of One4Life because it is more straightforward or less time-consuming. However, we agree that Eternis S is the more affordable, and thus, it is the more attractive choice.

Cybex Eternis S and Britax One4Life Design

Most car seats are very similar, and these two don’t look very different. The seats are made of plastic primarily for the base and cup holder, foam for padding, and fabric for the cover. The seat’s base is shallower than the width of the seat, but in comparison, Eternis S is slightly wider or 19.5 inches on the cup holders, while One4Life is 19 inches wide. The seat pan of Eternis S is 14.5 inches and 12 inches for the One4Life.

The harness height is adjustable to accommodate the child’s growth. The highest it can go in One4Life is 19 inches or 18 inches for the Eternis S. The total weight of the seat is 30 pounds for One4Life and 21 pounds for the Eternis S. Like most car seats, the fabric and padding are removable from the seat for easy cleaning with gentle detergent. The plastic part is easy to clean with a damp cloth.

Cybex Eternis S Installation 

One of the crucial parts of a car seat is the installation because they need a secure position. To install Eternis S, parents will have to remove the seat padding to open the seat to find the lower anchor compartment. Take the connectors and strap, route it to the rear-facing belt path, and close the seat back. Face the seat towards the vehicle’s rear and recline the seat for rear-facing mode. Attach the anchors and push the seat firmly, then pull one edge of the strap to fasten it.

The method for using a lower anchor for front-facing mode is similar, but the belt routing part is different. Parents can secure the seat using anchors or a seat belt, and in the front-facing mode, we may use the tether strap on the back of the seat. It is not the most effortless installation process but manageable.

Britax One4Life Installation

We prefer the One4Life installation because there is no need to open the seat cover manually. The seat opens from the front, which exposes the belt storage and path. Take out the belt and connector from the seat and extend the strap. Make sure it lays flat and connects both sides of the anchor to the vehicle. Press the seat and tighten the belt, then close the seat again. Closing the seat is very easy as it opens and closes with a click.

The seatbelt installation is the same, but now the seatbelt is routed in place of the lower anchor. For front-facing, the belt route is near the back of the seat, and you can easily route it using the lower anchor or the seat belt. The best part that makes installing One4Life faster and more straightforward is due to the ClickTight feature. This feature opens the front of the seat with a press of a button, so parents don’t need to remove the cover and harness manually.

Cybex Eternis S and Britax One4Life Fitting

Next, we want to talk about the fit of Cybex Eternis S and Britax One4Life. Many convertible car seats start from 5 pounds, so they should be able to fit newborns, and this is true for these seats. We found them to secure newborns nicely with the insert. Babies with a height of around 20 inches can use the seat’s lowest setting, and if your baby is smaller, we can add padding on the crotch strap. The head support of Cybex is not as thick, so parents may have to tweak the fit.

The seat specs are very similar because children from 5 pounds to 50 pounds can use the seat in rear-facing mode, but the height limit is around 49 inches. The front-facing method with a harness is from 22 to 65 pounds and up to 49 inches tall, while the booster mode height range is from 44 to 63 inches tall for One4Life or from 44 to 57 inches tall for Eternis S. We found the seats to fit children in early elementary school well.

Surprisingly, children with a height of 47 inches can still use the harness of One4Life, while in Eternis S, the kids who are around 44 inches tall are already using the car’s seatbelt. The headroom and height adjustment of One4Life is noticeably higher than Eternis S, which makes it last longer.

Cybex Eternis S and Britax One4Life Features

As for the features, some Cybex car seats have buckle sensors, but the model we have today is not. However, this Eternis S has L.S.P, a side protection panel to help reduce side impact by up to 25%. On the other hand, our favorite feature in One4Life is the ClickTight. This feature allows the seat to open up conveniently and exposes the lower anchor compartment with the routing paths. It snaps back quickly, and parents don’t need to remove the harness or padding.

Cybex Eternis S Vs Britax One4Life

There are many good car seats to consider, and these two are some of the most exciting options. The main difference is in capacity and ease of installation because we like how One4Life offers a higher convenience with its ClickTight feature. It also has a taller height adjustment and higher weight capacity for older or taller kids. But, the price is significantly higher than Eternis S, so parents may want to balance the budget and features.

- Rear-facing from 4 lbs. to 50 lbs. Forward Facing from 22 lbs. to 65 lbs., Belt-positioning Booster from 40 lbs. to 120 lbs.
- Adjustable Linear Side-impact Protection (L.S.P. System) absorbs up to 25% more impact forces in the event of a side impact collision*
- Patented 3-position reclining headrest helps prevent the child's head from falling forward while asleep, keeping the head and neck in a safe position and ensures a comfortable sleeping position
- 12-position, height-adjustable headrest with an integrated no-rethread harness for protection that grows with your child
- 10 years of use: New one4life convertible to booster car seat grows with your child from 5 to 120 pounds & up to 63 inch tall
- Install confidently: With a ClickTight installation, you'll know it's right in 3 easy steps
- One4life: Converts from rear facing infant car seat, to forward facing 5 point harness, to high back belt positioning booster
- Britax safety: High strength steel frame, crumple zone helps absorb crash energy and patented v-shaped tether


If parents don’t have an issue with the budget, we recommend getting Britax One4Life for ease of use. Installing a car seat can be time-consuming, especially if parents have to mount the seat in different cars. The One4Life is quick and easy to use while providing a higher capacity to last longer.