Start with the function
Ask what the packaging must do: cushion, locate, wrap, bundle, protect from dust, support presentation, stack or survive transport. Material selection should follow the function rather than a marketing label.
Then define constraints
Consider product geometry, weight, moisture, handling, machine process, storage, transport, appearance, disposal route and cost target.
Practical rule: moulded pulp, kraft paper and shrink film solve different problems. In some projects they may also be used together as part of one packaging system.