For young infants, the seat used is an infant carrier with typical weight recommendations of 5-20 lb. Most infant seats made in the US can now be used up to at least and , with some going up to . In the past, most infant seats in the US went to and . Infant carriers are often also called "Bucket Seats" as they resemble a bucket with a handle. Some (but not all) seats can be used with the base secured, or with the carrier strapped in alone. Some seats do not have bases. Infant carriers are mounted rear-facing and are designed to "cocoon" against the back of the vehicle seat in the event of a collision, with the impact being absorbed in the outer shell of the restraint. Rear-facing seats are deemed the safest, and in the US children must remain in this position until they are at least 1 year of age and at least . although it is recommended to keep them rear-facing until at least 2 years old or until they outgrow the rear-facing car seat height and weight, whichever is longer.