I was constantly searching for the perfect diaper cover. I truly believe this design fits the bill for both. What makes it unique is the length in the rise and the width of the back to give full coverage. Because of these two factors, your baby will be able to wear them much longer regardless of the weight.
The cover features soft,deep leg gussets to contain blow outs and is gathered across the front to prevent tights, pants, and the like from getting sucked in and soaked.
I recommend ordering according to age of the baby, regardless of weight. As an added note, if you have to double diaper your little one, you might consider going up one size to accomodate for the added fluff. :)