Eternis S - More Info

Product Information

  • Length:

    Rear-Facing: 32 in Forward-Facing: 25.25 in


    Rear-Facing: 22-25 in Forward-Facing: 19.75-22 in


    Rear-Facing: 19in Forward-Facing (Fully upright): 25.5-29.5 in

  • Weight:

    26 lbs

  • Maintenance:

    Machine washable COLD, delicate cycle, mild detergent. Hang dry. For more information, see user manual.

  • Engineered and designed in Germany

    Engineered and designed in Germany

The pictures of products and the measurements on this website are for indication purpose only. Products may vary and we reserve the right to make product changes.


Will this car seat fit my child?

The Eternis S is designed for children between 2.3 -54.4kg (4-120 lbs.) with a height between 43.2-144.8 cm (17-57 inches).

Will the Eternis S convertible car seat fit my vehicle?

CYBEX does fit checks on a variety of vehicles. Due to variations in make, models, and years of manufactured vehicles, it is encouraged to try the seat in your vehicle at a retail location nearest you. You should try both rear facing and forward facing modes and in different locations (outboard rear seat, vs middle seat). CYBEXCYBEX recommends getting your seat checked by a Certified Child Passenger Safety Technician. You can find this free service by visiting to find a seat check nearest you.

Does the Eternis S convertible car seat have an expiration?

Every car seat has an expiration due to Regulatory changes and technology enhancements in child passenger safety. The Eternis S convertible car seat has been certified for 10 years of use. Once your car seat has reached its expiration date, we recommend recycling the seat by contacting your local community recycling center.

How much does the Eternis S convertible car seat weigh?

The weight of the car seat (excluding the infant positioning pillow is 11.8 kg (26 lbs)

How big is the Eternis S convertible car seat?

The seat will vary in height and depth depending on the recline angle and headrest position. The seat with headrest down and in the upright position is 63.5 H x 51 W x 64.2 cm (25.5” H x 20” W x 25.3” D inches)

What fashions are available for the Eternis S convertible car seat?

The Eternis S is available in Pepper Black, Manhattan Grey, Lavastone Black, and Denim Blue.

Where is the Eternis S convertible car seat available for purchase?

You can find the nearest retailer on our website at

Where do I store/find my Lower Connectors on my Eternis S convertible car seat?

The lower anchor connectors of the LATCH system are displayed outside of the seat in the seating area when you first receive your Eternis S convertible car seat. You should store the lower connectors inside the seat when not in use. The storage location is located below the seat under the car seat cover. Simply pull the cover toward the front of the car seat and a compartment should be visible. Open the compartment to store your lower connectors. The storage area will also fit the buckle when not in use (booster mode).

Where do I store my Tether on my Eternis S convertible car seat?

The Tether, used for forward facing installations, can be found on the back of the Eternis S, located behind a snap door. To gain access to the Tether, simply open the door and pull out the tether. The tether should always be used for forward-facing car seat installations, whether you install the car seat with the lower anchors (up to a child’s weight of 40 lbs) or the vehicle’s seat belt. The tether should never be used in rear-facing mode.

Is it safer to use lower anchors or the vehicle’s seat belt?

The safest installation method is always the one that allows you to install the car seat correctly. Both methods, if used in accordance with the child safety seat manual and vehicle’s owner’s manual requirements, provide equal protection.

Can I install the Eternis S convertible car seat using both lower anchors AND the vehicle seat belt?

No. You can use the vehicle seat belt or lower anchors. The Eternis S should be installed using only one installation method.

How do I know if I have LATCH available in my vehicle to install the car seat?

Most U.S. vehicles manufactured on or after Sept. 1, 2002, are equipped with LATCH. Refer to your vehicle owner’s manual under the Child Restraints section to confirm.

Do I have to use the vehicle seat belt installation method?

The Eternis S allows for the use of LATCH up to 15.9 kg (35 lbs) in rear facing and up to 18.1kg (40 lbs) forward facing. However, the vehicle may have additional limitations. Always refer to both your car seat manual AND your vehicle owner’s manual, typically under Child Restraint or Child Safety in the index. To determine the maximum weight permitted to use the lower anchors, you should refer to both the vehicle and child car seat manuals. In the event the two differ, use the lower limit as the deciding factor. You may use lower anchors in rear facing or forward facing mode on the Eternis S until the allowable weight limits or when you reach the limits of the vehicle anchors, whichever comes first. When you can no longer use lower anchors, the car seat must be installed using the vehicle’s seat belt. For forward-facing installations, use the top tetherif of the LATCH system.

Can I use the lower anchors in the rear center seat?

While most vehicles allow for a center seat installation with the vehicle’s seat belt, there are some makes and models that do not allow for lower anchor installation in the rear center seat. You should refer to the vehicle owner’s manual for center seat lower anchor installation. If the manual does not specify, or is not clear, it is recommended to contact the vehicle manufacturer for clarity. CYBEX allows lower anchor installations in the center seating position as long as the width of the lower anchor bars in the vehicle is between 11 – 20”.

When should I use the Tether for installation?

The tether should always be used in forward facing installations. The tether can be installed whether using the lower anchor or seat belt installation when forward facing. Never use the tether in rear-facing mode.

Why is it important to use the Tether for forward facing installation?

The use of a tether can help achieve a tighter installation to help reduce the risk of injury by reducing the distance that your child’s head moves forward in the event of a crash. The tether should be used for forward-facing installations with either the lower anchors or seat belt. For proper installation, please refer to both the child safety seat manual as well as the vehicle’s owner manual.

I cannot find the Lower Anchors on my vehicle for LATCH. How can I find them?

In some cases, the lower anchors may be recessed within the vehicles seats. If your vehicle was manufactured after September 1, 2002, the vehicle should be equipped for LATCH. In most cases, there should be icons near the locations of the anchors. However, it is best to refer to the vehicle’s owner manual to help identify the locations.

How do I uninstall the lower anchor connector from my Vehicle anchor bars?

To remove the seat from the vehicle when using lower anchors, it is best to loosen the webbing first. Push down on the adjuster button while lengthening strap. Once the tension has been released, you simply pull the red loops for the lower connectors.

How do I uninstall the tether anchor connector from my vehicle anchor bar?

To remove the tether, press the adjuster release button to loosen the strap. Squeeze the hook with your thumb and finger and unhook.

Where do I route the vehicle’s Seat belt in the Eternis S convertible car seat?

There are two areas to route the vehicle’s seat belt through the Eternis S. The rear facing belt path is under the car seat cover near the front of the car seat and is labeled with blue decals. The forward-facing routing is under the car seat cover near the back of the car seat and is labeled with red decals.

What are the blue and red plastic pieces near the belt routing decals?

The Eternis S has 2 sets of Lock-Offs, blue for rear facing and red for forward facing, that are located on either side of the Eternis S. The lock-off allows you to easily install the Eternis S convertible car seat with the vehicle’s seat belt and belt locking mechanism.

How do I use the lock-offs on my Eternis S convertible car seat?

Route the vehicle seat belt through the proper belt path (blue for rear-facing, red for forward-facing) and buckle the seat belt. Check to make sure the seat belt is not twisted. Once you have routed the vehicle seat belt through the rear facing or forward facing belt paths, but before tightening the vehicle belt, slide the shoulder belt portion of the vehicle’s seat belt through the Lock-Off on the opposite side of the vehicle buckle. For vehicles equipped with a locking retractor, pull the remaining seat belt out of the retractor and feed it back (Belt retractor should make clicking sounds as you feed it back). Push down on the Child Seat and pull the vehicle shoulder belt through the lock-off to tighten. See the instruction manual for complete instructions and illustrations to guide you.

Do I have to use the lock-offs on my Eternis S convertible car seat?

If your vehicle has a lap-only belt with a locking latch plate, you will not utilize the lock-off on the Eternis S for rear-facing or forward-facing seat belt installations.
If your vehicle has lap-shoulder seat belts, the lock-offs should be used along with the of locking mechanism for the vehicle seat belt.

How long do I use the infant insert?

The Infant insert is used to ensure better fit for smaller children (infants). It can be removed once the smaller child fits the car seat and harness properly without the need for the insert.

Do I have to use the infant insert?

The purpose of an Infant positioning pillow is to ensure a snug fit when harnessing your small child, if needed.

How do I know if my child is properly positioned in the Eternis S?

Place the child in the car seat with their back and bottom flush with the seating surface. Adjust the headrest to its lowest position. The shoulder straps should be positioned at or below the child’s shoulders for rear facing, and at or slightly above in forward facing modes.
Conduct a pinch test to determine a snug harness fit: the middle finger along with the thumb and forefinger pinch the strap where it comes over the shoulder. Place your middle finger under the harness webbing to pull it up slightly, then use the other two fingers to pinch. If there is no excess webbing, the harness is snug. If you can find excess webbing that can be easily folded, then the harness is too loose.

When should I move my child from rear facing to forward facing?

The American Academy of Pediatrics recommend children remain in a rear-facing car safety seat until your child exceeds the maximum weight or height of their car seat for rear facing. For the Eternis S, this would be 22,6 kg (50 lbs) or 121.9 cm (48”).

Where is the Eternis S manual located?

The manual is located on the back of the car seat behind a snap door. To gain access to the manual, simply open the door and remove the manual. Before installing the Eternis S, always refer to the child seat manual as well as the vehicle’s owner manuals for important instructions regarding proper installation. It is always recommended to keep the car seat manual with the car seat for easy reference.

If I lost my manual, where can I get a new one?

Manuals can be found online at . Simply click at the top right to select the category and model.

Do I have to register my seat?

CYBEX and NHTSA recommend all users register their car seats to receive important updates or recall notifications. This information cannot be used for marketing purposes. You can register your Eternis S in one of three ways: using the postage-paid postcard attached to the car seat at purchase, entering the information online at or via the SensorSafe application link.

Can the Eternis S convertible car seat hang over the edge of the vehicle seat?

The Eternis S base (bottom in contact with vehicle seat) can overhang the vehicle seat by no more than 20%. This amounts to no more than 3”. Ensure the seat base (bottom) is positioned flat against the vehicle seat and is properly reclined prior to measuring.

Can I use the seat on aircraft flights?

The Eternis S child seat Restraint is Certified for Use in Motor Vehicles and Aircraft when used in harness mode. This information is listed on a label on the bottom of the seat and in the car seat manual. When used as a belt-positioning booster seat the Eternis S is only certified for use in motor vehicles. As a booster seat the Eternis S is not certified for use in aircraft.

How do I know if my car seat is installed at the correct recline?

The Eternis S is equipped with two recline level indicators to assist with installation recline (one in Spanish and one in English). To ensure the best results, it is important that the base of the car seat (Bottom) lays completely flat against the vehicle seat prior to using the recline indicators. To use the indicators for recline, look for the silver ball in the clear windows. When in rear facing mode, the metal ball should be in the blue areas of the indicator. When forward facing, the metal ball should be in the red areas of the indicator.
Recline positions 1 – 4 should be used in rear-facing mode. Recline positions 5 – 6 should be used in forward-facing mode.

How do I know if the seat is properly secured?

To check the installation, hold the car seat at both sides near the belt path (where you have the seat installed) and pull side to side and front to back. The car seat should not move more than 1 inch (2.5 cm) from vehicle seat back or side-to-side. If it moves more than 1 inch, try tightening the vehicle seat belt or lower anchors. Make sure you add the tether anchor for forward-facing car seat installations. If the car seat still is not tightly installed, try another seating position, or switch to a different installation method (lower anchor or seat belt).