Head huggers are designed for use in car seats, but can also be used anywhere babe needs extra support. It's very important to remember when using Head Huggers, that they are to be inserted into the car seat, stroller, etc. AFTER babe is all buckled up; therefore, not interfering with the harness system. They are for comfort, not for safety and are made from soft minky.
Standard Head Huggers fit in most car seats and are for newborns to 6 months.
Slim Head Huggers are for deeper and narrower car sets, like BOB B, Peg-Perego car seats, and can be used when babe is older for a little extra support.