Leigh-Ann, Child Passenger Safety Technician:
The Baby Bloak™ is a great product because it lets the car-seat do its job
– with the Baby Bloak™ there is no extra fabric between the child and
the safety harness.
As a Child Passenger Safety Technician, I’d recommend using the Baby
Bloak™ as a safe way to keep your little one warm in the car. I use the
Baby Bloak™ for my son Levi, because I know he is both safe and warm!

Baby Bloak works over straps to
keep your child snug, safe, and warm.

Using coats in the car seat loosens straps.  In the event of an accident, the coat could compress, allowing your child to slip out of his straps and be ejected from the seat.

The National Transportation Safety Board, 
The Children's Hospital of Philadelphia, and
Car-Seat.org all recommend against using coats, blankets, and bundling systems under car seat restraints.