Thirsties® Duo Wraps are a result of more than six months of development and testing.  This affordable wrap actually hatched as a one-size diaper cover.  Logically, we thought a one-size diaper cover would be the most affordable option for the end-consumer.  But what we actually discovered, no matter how many different cuts and protoypes we made, is that the 'one-size' options are too big on the average newborn and too small for most toddlers over 24 months of age. What this means is that the 'one-size' option truly only fits your baby properly when your he weighs between 10 lbs to 32 lbs.  Alas, our findings confirm that the label 'one-size' diaper/cover simply does not live up to its claim.  Most families purchasing a 'one size' cover would actually end up purchasing a newborn size, a 'one-size', and a toddler size:  THREE sizes from birth to potty!  Not ONE.  Therefore, in the end, Thirsties® Duo Wraps are truly looking out for your wallet.