Jeff Lupient describes the different kinds of rear-facing car seats.

Jeff Lupient: A Parent's Guide on Rear-Facing Car Seats

There are three types of rear-facing seats. These are rear-facing only, convertible, and all-in-one. According to Jeff Lupient, the AAP recommends that all infants ride rear-facing seats starting with their first ride home from the hospital. In addition, all infants and young children must ride in a rear-facing seat for as long as possible or until they reach the maximum weight and height their car seat manufacturer allows.

Most convertible seats allow children to ride rear-facing for two years or more. Jeff Lupient further explains that as children reach the maximum weight, height, or length allowed by the manufacturer for their rear-facing–only seat, they must continue riding rear-facing seats in a convertible or all-in-one seat. It means that when infants outgrow their rear-facing–only seat, a convertible seat should be installed rear-facing.

Rear-Facing Only

Rear-facing seats are used for infants 22 to 35 pounds and 26 to 35 inches. It depends on the model. Most models are small and have carrying handles. They also usually come with a base that can be left inside the car. The seat clicks into and out of the base; thus, installing it each time is unnecessary. Jeff Lupient says parents can buy more than one base for additional vehicles.

Rear-facing cars should be used only for a child's travel. It's not for sleeping, feeding, or any other activity outside the vehicle.

Some models of rear-facing car seats include load leg or anti-rebound bars. These help absorb the energy of a crash. Load legs decrease forward rotation in the initial phase of a crash. The anti-rebound bars protect the child during the second phase of a crash from rearward rotation.

Convertible

Convertible car seats can be rear and then converted to forward-facing when children outgrow the weight or length limit for rear-facing. It means convertible car seats can be used longer by your child. 

Jeff Lupient also mentions that convertible seats are bulkier than infant seats. They don't come with carrying handles or separate bases. They are also designed to stay in the car.
Many convertible car seats have higher limits in rear-facing weight, up to 40 to 50 pounds. This feature makes convertible seats ideal for babies who are bigger and toddlers.

Convertible car seats have a 5-point harness that attaches at the shoulders, the hips, and between the legs.

All-In-One

Parents can use all-in-one car seats for rear-facing, forward-facing, or even as a belt-positioning booster. It also means your child may use the seat longer as they grow. This type of car seat is often bigger, so you'll have to check if they fit in the vehicle when rear-facing.

All-in-one car seats don't have a carrying handle or separate base, but like convertible car seats, many models have higher limits in rear-facing weight of up to 40 to 50 pounds.

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