The cardboard must be rigid and dense enough to resist puncturing or bending. If layers of corrugated board are used, some conservators recommend placing each sheet with the grain perpendicular to that of adjoining layers for increased rigidity. It is better to use crates for large objects. If they are sandwiched, very thick or dense boards must be used, and wooden cross pieces may be advisable. The sandwich package should be sealed at the edges with tape and wrapped with a sturdy material such as Kraft paper.
Crates afford more protection than sandwiches and are usually the better choice.
They are necessary for books and other three-dimensional or heavy objects, for large numbers of artifacts, or for objects that need ample cushioning. Although waterproof containers can be made at great cost, ordinary wood crates are not waterproof or even water resistant. The most you can expect from the average well-made crate is physical protection. To ensure that the contents are not exposed to rain or other hazardous conditions, you must use a reliable carrier. Each object should be wrapped and packed so it does not slide around in the crate.