Body and personal care products are used more often, in larger volumes and frequently in a wet environment. That shifts the priorities: a pump that feels right at 30 ml can feel slow at 300 ml, and a closure that opens easily with dry hands may not with wet ones.

Volume also makes material a commercial question rather than only an environmental one. At these quantities, weight per unit and material choice show up directly in cost, which is why PCR content and mono-material structures tend to be discussed here first.