Diaper sizing and quality differences are more concrete and checkable than the marketing on the package suggests.
Size by weight, not age
Diaper sizes are based on weight ranges, and babies grow at different rates — an age-based guess is a much less reliable way to pick a size than actually checking your baby's current weight against the specific brand's size chart, since weight ranges for the same labeled size can vary somewhat between brands. Sizing up is generally better than sizing down if a baby is between sizes — a diaper that's slightly loose is a minor inconvenience; one that's too small can mean poor containment and leaks.
What actually separates cheap and premium diapers
The core differences tend to come down to absorbent material quality and distribution, the elastic and fit around the legs and waist, and the wetness indicator's reliability. A well-designed diaper distributes absorbed liquid evenly rather than pooling it in one spot, and fits snugly enough at the legs and waist to prevent leaks without leaving red marks or feeling restrictive. These differences are genuinely noticeable in daily use, not just marketing language — though the "best" diaper for a specific baby's body shape can still vary by brand, since fit depends partly on individual proportions.
Overnight diapers trade dryness feel for absorbency
Overnight-specific diapers are built with extra absorbent capacity to handle a longer stretch without a change, which usually means feeling less immediately dry against the skin right after use compared to a daytime diaper designed to be changed more frequently. This is an intentional design tradeoff, not a lower-quality product — it's built for a different use case than a standard daytime diaper.
The one thing people forget
Don't buy a large bulk supply of a size you haven't tried yet, especially with a new brand — babies can react differently to different diaper materials or fits, and buying just enough to test a new size or brand before committing to a large pack avoids ending up with an oversized stash of diapers that don't actually work well for your baby.