Shrunk at first! Good though
I wasn't sure whether these would make loads of difference and I expected a really bulky nappy. But after having bought 5 I have found them very handy. My baby is a big milk drinker (breastfed) and I was changing nappies 2 times at night, this is down to the once or not at all now. For a nearly 4 month old. Also they bulk out the nappy a bit, but it still fits comfortably under a body and sleepsuit.
These boosters don't say they fit size 1 pocket nappies, but after the first wash, they shrink and fit well (see picture).
Note that they haven't shrunk since this so it's obviously just a one time thing.
Wouldn't put a booster in every nappy or you are less likely to change baby often. Love my collection!