There are many types of car seat bunting to choose from. Buntings offer an advantage over blankets, since they cannot be kicked or fall off. You should not, however, put a coat or bulky snowsuit on your baby while he or she is in a car seat.
All car seat manufacturers recommend against using coats and snow suits in cat seats. This is because the straps cannot be adjusted properly when the baby is wearing bulky clothing. In an accident, the coat will become compressed and the baby can come out of the seat. A car seat bunting is a great way to avoid a coat or snowsuit and still keep your baby warm.
One type of car seat bunting available is strapped to the seat with the shoulder and lap straps. This puts a layer of the bunting between the baby and the back of the car seat. Similar to coats, the car seat straps with these buntings cannot be properly adjusted to contain your baby in the event of an accident. Some car seat manufacturers discourage the use of these buntings, and doing so may void your warranty.
There are plenty of safe options available to keep your baby warm. Snowsuits and coats made of Polartec® fleece are fine to use with car seats. Since they are not bulky, the straps can be tightened properly. Polartec® fleece is very warm, despite being thin.
One type of car seat bunting fits over the seat like a shower cap, and there is a hole in the top for baby's face to fit through. There is often a flap over the hole that can be closed to keep out wind and cold. Since these buntings fit over the top of the seat, they do not affect strap tightness or safety.
Another type of car seat bunting is worn by the child like a poncho. It straps around the child's shoulders, and the rest fits over the seat. Putting the poncho on after the child is in the seat prevents strap interference.
Car seat buntings can be expensive but are great to have in colder climates. There are patterns available for making your own which are simple to follow even for people who are not good with crafts. A poncho can be made with very minimal sewing.
It can be possible to use a plain wither coat safely with a car seat. Put your child into his or her car seat with a coat on, unzipped. Pull the child's arms and coat through the arm straps. Tighten and fasten the straps as usual, and then zip the coat over the straps. This will prevent loose straps, and the coat can still be worn.