In Depth Baby Product Reviews Led by a Pediatrician
We buy all the products we test — no freebies from companies. If you purchase through our links, we may earn a commission, which helps support our testing.
The Cybex Eternis S is one of two Cybex options we tested in our best convertible car seat review. It was the lower scoring of the two. The Eternis offers better than average crash test analysis, is easy to use, and offers much for comfort and quality. In many ways, it looks good on paper and in real life. Unfortunately, this seat is harder to install in our testing than most competition. Whether it is the LATCH method or the vehicle belt, neither option was straightforward, and we had some trouble getting the seat tight, and visibility was hindered. This Cybex earned just above average for the group, and while that is still better than many, it didn't perform well enough in any test to justify making it a number one choice.
REASONS TO BUY
Better than average crash test analysis
Better quality
Ease to use
SIP claims
Cup holder
REASONS TO AVOID
Wider width
Harder to install
New with SensorSafe
Cybex has released a new version of the Eternis now with SensorSafe. We believe this is the only change to the seat, but we did not test this version of the seat. The only change we can identify is the chest clip with SensorSafe technology. We now link to the version with SensorSafe.
This comfy option was harder to install, and it resulted in a lackluster overall feel
Easy to install and use and one of the best crash test analysis scores make this seat a winner for most families
Better crash test analysis and a lower price make this easy-to-install seat an award contender that just missed the mark
Wallet-loving price on a seat that is easy to install and earned better crash test results than most
Despite a lack of padding and a harder LATCH install, this inexpensive option earned impressive crash test results, making it a winner for budget-limited families
Rating Categories
Cybex Eternis S
Graco 4Ever DLX
Graco Extend2Fit 3...
Graco SlimFit 3-in-1
Evenflo Tribute 5
Crash Test(35%)
7.8
8.8
8.6
8.5
8.6
Ease of Installation - LATCH(20%)
6.1
7.9
7.8
7.9
4.3
Ease of Installation - Belt(15%)
5.6
7.1
6.4
6.5
5.6
Ease of Use(15%)
7.5
8.0
7.0
7.5
5.0
Comfort/Quality(10%)
7.5
6.5
8.5
8.0
3.0
Weight/
Size(5%)
6.5
7.5
7.5
7.1
7.8
Specs
Cybex Eternis S
Graco 4Ever DLX
Graco Extend2Fit 3...
Graco SlimFit 3-in-1
Evenflo Tribute 5
Min/Max Rear Facing Passenger Weight
4-50 lb
4-40 lb
4-50 lb
5-40 lb
5-40 lb
Min/Max Forward Facing Passenger Weight
22-65 lb
22-65 lb
22-65 lb
22-65 lb
22-40 lb
Rear Facing Maximum Height
Top of head must be 1 in from the top of the headrest
Top of head must be at least 1 in below handle
Top of head must be at least 1 in below handle
Top of head must be at least 1 in below handle
37 in
Forward Facing Maximum Height
Top of ears are below the top of the Headrest
49 in
49 in
49 in
40 in
Weight
27.0 lb
21.8 lb
20.5 lb
18.5 lb
9.4 lb
Minimum Rear Facing Length
27 in
25 in
26 in
28 in
29 in
Minimum Seat Width
20 in
19 in
19 in
19 in
18 in
Number Of Recline positions
6
6
6
4
1
Shoulder Harness Positions
12
10
10
10
4
Crotch Strap Positions
2
2
2
3
2
Anti-rebound Device
No
No
Yes
No
No
Head Support
Yes
Yes
Yes
Yes
Yes
Infant Positioning Insert
Yes
Yes
Yes
Yes
No
Harness Type
No-rethread
No-rethread
No-rethread
No-rethread
Rethread
Onboard Manual Storage
Yes
Yes
Yes
Yes
Yes
Rear Facing Level Indicator On Seat
Bubble, both sides
Bubble, one side
Bubble, one side
Bead, one side
Line on decal, both sides
Booster Mode Available
Yes
Yes
Yes
Yes
No
Foam Type
EPS
Not mentioned
Not mentioned
EPS
EPS
Seat Lifespan
10 years
10 years
10 years
10 years
6 years
Aircraft Certified
Yes in harness mode, No in booster mode
Yes in harness mode, No in booster mode
Yes in harness mode, No in booster mode
Yes in harness mode, No in booster mode
Yes
Warranty
2 year limited
1 year limited
1 year limited
1 year limited
90 day limited
Show full specification details ▼Hide full specification details ▲
Our Analysis and Test Results
German company Cybex is a part of Goodbaby International Holdings Ltd. They focus on developing functional gear with a concentration on safety and design. Cybex sells favorite car seats, highchair, bouncer, and strollers.
Performance Comparison
The Eternis earned a slightly above-average crash test analysis score based on the sensor data obtained in our commissioned crash tests.
Credit: GearLab & MGA Research
Crash Test
The Eternis earned a slightly above-average score from crash test analysis in our tests. This makes it a better-scoring Cybex option but not quite good enough to break into this lineup's upper echelon of possibilities.
The Eternis has a side-impact feature that pops out for use if the seat next to the Eternis is not occupied by a human.
Credit: Abriah Wofford
All the convertible seats we tested should meet federal guidelines and are considered safe. We had our tests performed on a more modern sled and at a faster speed to identify the big dogs in this group.
This Cybex managed a better-than-average final analysis and has the better Cybex convertible seat score of the two we tested. Given our hotter test, this is nothing to sneeze at, even if it couldn't keep up with the big dogs in our lineup.
The graph here is a comparison of the recorded crash test chest clip sensor data of the Eternis and the Graco 4Ever. The Graco was one of the top performers.
This graph of the crash test results of the HIC sensor shows the comparison of recorded data for the Eternis vs. the Graco 4Ever DLX.
The head sensor results were some of the lowest in the group (lower is better), which helped its overall analysis, as its chest clip G-forces result was closer to the average.
We had to kneel in the Eternis seat to get the right angle on the LATCH strap to tighten it.
Credit: Abriah Wofford
Ease of Install - LATCH
Neither installation method is ideal for the Eternis, but the LATCH method is better than using the vehicle belt. The Eternis has flexible strap push-style connectors with easy remove pull tabs. There is no belt lock-off, but bubble-style angle indicators are on both sides.
The Eternis level indicator is a ball in a channel, and it is easy to read, but we wish the range lines on the indicator were bigger.
The angle recline adjustment is on the foot of the seat, and while it works well, it is harder to access in the rear-facing configuration when it is pressed against the vehicle seat.
The recline adjustment is the standard fare of the handle on the foot portion. It rotates smoothly back and forth, but the location is a poor choice despite its commonality.
The Eternis LATCH connectors are push-style with a red pull loop for removal.
Credit: Abriah Wofford
The Eternis LATCH connectors do not make a reassuring click when they connect, which we suspect many parents will be listening for. The level indicator is color-coded and confusing, so be sure to pay special attention to it, as we felt it was somewhat misleading. Each connector has its own strap for tightening, and the manual offers good advice for getting the job done easier. It feels stable once installed, but there are more steps and opportunities to mess up the process than with most seats.
Pulling the release tab on the LATCH connectors requires significant effort, and we really had to put our bodies into it to get it done. This is probably to avoid accidental releases.
The forward-facing installation of the Eternia has a flexible strap and push-style connectors. It uses the same bubble level indicator on both sides, and there is no lock-off. The connectors require some digging to find in this position, but threading through the sides was straightforward with no obstructions. Our indicator was right on the edge of being acceptable, and the seat was wide, making access to connectors more of a challenge. Both sides have their own tightening buckle, and you have to ensure they don't interfere with tightening. We had trouble getting the seat tight in both test cars, and while it passed the wiggle test in both, it wasn't much to write home about.
Because the Eternis is so wide, it takes some effort and entry into the vehicle to attach the belt to the buckle.
Credit: Abriah Wofford
Ease of Install - Belt
Using the vehicle belt to install the Eternis would not be our top choice. While neither option is easy, LATCH is the way to go here if you can swing it and the manufacturer guidelines allow it in your situation.
You need to lift the back pad to access the belt pathway to thread the straps through for forward-facing installation.
The Eternis lock-off for forward facing is somewhat hidden and requires some practice to get right.
There is a bead level indicator on both sides of the seat for convenience for rear-facing installation. The belt pathway is not color-coded on the Eternis, but there is a belt lock-off to help get things tight. Threading is initiated by pulling the Eternis fabric to the front to see and access the pathway, creating a small barrier to overcome to get the job done. It is easy enough, but it could be improved with color coding to clarify the pathway. It has a wide range of reclines acceptable for installation. The cup holder got in the way of installation, and we moved it to the far side to keep it out of the way. The bead in the indicator seems to get stuck and doesn't move as freely as we expected. We had to get in the car and crouch low to see the locking mechanism, but the profile was low, so even petite users could reach over to buckle the belt on the opposite side. The lock-off is a slit with grooves, so you have to shimmy the webbing of the belt in place, which means you can't thread it and then pull it tight; you have to take out most of the slack before putting it through the slit and then locking it in pain. The final installation of the Eternis is pretty stable and didn't wiggle much from any angle.
The belt pathway on the Eternis is not color-coded, though it does have sticker indicators to assist you.
The rear-facing configuration of the Eternis is located under the seat portion of the seat near the base.
The Eternis forward-facing installation includes a bead indicator and a belt lock-off but no color coding. This seat consists of a flap to flip up, and it is stiff and won't stay out of the way. It kept falling down during testing, making us feel like we were flying blind behind the cover. Adjusting the recline is easy, and there is a wide range of options for the Eternis. The belt threads through the back easily, but you have to push your hand through to undo the lock-off. The lock-off is a small clasp that works well but is tucked back and feels hidden from the installer. You must tighten the belt and lock it off before letting the tension out. It didn't feel as stable, and if there hadn't been a flap or the lock-off easier to see, we suspect it could have been more stable. Overall, it isn't terrible, but there were lots of little things that were poorly designed that made this seat harder to install using the vehicle belt than it should have been.
The Eternis has a unique headrest tilting feature.
Credit: Abriah Wofford
Ease of Use
The ease of use for this seat is better than average, and we don't think any feature will cause significant frustration.
The Eternis buckle and chest clip are fairly standard, but both the buckle button and chest clip release are small compared to easier-to-use options.
Credit: Abriah Wofford
Harness
The Cybex has a big buckle that is easy to push in prongs. The button is harder to push to disengage, and it could be problematic for those with wonky thumbs. There are magnetic retainers to hold the prongs in place so they don't get lost. This is a cool feature, and the magnet is strong, but the prongs are so small it takes some finessing to connect the prong to the magnet.
The Eternis harness adjustment is unlike most of the competition and is located on the back of the seat, not the top of the headrest.
Credit: Abriah Wofford
To tighten the Eternis, there is some resistance, and we really had to tug it toward the end to get a snug fit. It isn't the easiest, but it isn't so complicated you'll be annoyed. The release button is easy to push and is further back than most, but we could still use our thumb to operate it.
The Eternis headrest can tilt back and forth. This is one of the only options we've ever seen like this.
Credit: Abriah Wofford
The harness height adjustment on the Eternis is a non-rethread style with twelve height adjustment levels and two crotch positions. We were able to adjust the buckle strap from above. The shoulder height adjustment is two different adjustments for height and recline. The movement of the assembly is a bit jerky as it clicks into each level, but it isn't hard to do.
The LATCH connectors on the Eternis have a storage compartment under the seat bottom.
Credit: Abriah Wofford
LATCH Storage
The LATCH storage is under the seat padding on the Eternis. Compared to the competition, it is average, with a cubbie big enough for all the parts and no need for clipping the connectors in place. It is much easier than those requiring clicking in place and removing before use.
The Eternis has impact foam under much of the sides and the cover secures with snaps (seen here).
Credit: Abriah Wofford
Cover
The cover is quick and easy to take off. There aren't many buttons, and everything is fitted in slots so you can pull them out.
Putting the cover back on takes more effort, and you have to trace your hands along the edge to shove it into place. It takes more time, even if it is straightforward.
The Eternis has a clip-on cup holder that is easy to use but does get in the way of installation and might be better added after the seat is in place.
Credit: Abriah Wofford
Comfort/Quality
With an above-average score for comfort and quality, the Eternis is better than some but not as good as others in this lineup.
The fabric is smooth and doesn't feel rough in our tests. It is exceptionally smooth but fares well compared to the other options. There's nothing to crow about here, but it is a nice departure from rougher things. The infant insert has extra tushie padding and puffy side additions but nothing in the head area.
The Eternis has a manual storage pocket on the back of the seat. The forward-facing tether is also stored in this pocket.
Credit: Abriah Wofford
Overall, the padding has an initial impression of being plump and full. However, once pressure is applied, you can feel a lot of air release before you hit the less impressive padding. It is good, but just not as good as you think it will be. There seems to be more padding on the leg area than in the bottom portion. Overall, the padding isn't bad; it is just slightly above average once you get past the deceptive appearance.
The Eternis has a side impact additional feature, but its efficacy is not known since there is no standard side impact crash testing.
Credit: Abriah Wofford
The shell is relatively sleek looking, with a cubby for the tether and the LATCH system being the only parts that might be harder to clean. There is one cup holder you can place on either side, and the outside location makes it easier to detach to wash. Perhaps not as sleek looking as those integrated with the side, but certainly just as useful.
The Eternis is one of the widest options in the group, while the weight is largely average.
Credit: Abriah Wofford
Weight/Size
The Eternis is a big fella at 27 lbs. While perhaps not a deal-breaker if it will stay put in a single car most of its life, it likely is if you plan to carry it often or use it for travel. The average weight here is 24.3 lbs, and the lowest is closer to 9 lbs.
The Eternis is one of the widest seats in the group, with a width of 19.4 in. The average is 18.6, and some of the most narrow options are closer to 17.
Should You Buy the Cybex Eternis S?
The Eternis is neither great nor terrible, and it lacks any real standout feature or functionality to put it on the map. While we think most parents can use it without much complaint, it still pales compared to better seats in our review. Whether it is just the above-average crash test results or the harder-to-install design, it simply didn't meet expectations. Overall, we see why someone would be attracted to the seat, and we don't blame them, but there is more to be had elsewhere for the same or even less money.
What Other Convertible Car Seat Should You Consider?
If you want something better than satisfactory, the Graco 4Ever DLX is a top performer with standout functionality and the best crash test results in the group. With a slightly higher price than the Eternis, you are getting so much more for safety, comfort, and ease of installation that we don't think most parents will mind the few extra dollars. If budget is a concern, the Graco SlimFit 3-in-1 is a great seat that performed better than the Eternis in every metric test, including ease of installation, comfort and quality, ease of use, and more.
