A crib mattress is small and light, but bending or crushing it, even briefly, can leave a permanent crease that compromises the flat sleep surface an infant needs.
Pro tip: Pack the crib mattress in the same box or bag as the crib sheets so the first-night setup is a single grab, not a search.
Watch out: A crib mattress folded or bent for an extended period can develop a permanent crease that affects the safe, flat sleep surface it needs for an infant.