I can't seem to find an obvious choice by browsing product literature, which is my usual tactic. This is the concept I want a Spanish word for: https://en.wikipedia.org/wiki/Dunnage
With the context provided
inexpensive or waste material used to load and secure cargo during transportation
envoltorio would work:
recipiente o envoltura que contiene productos de manera temporal principalmente para agrupar unidades de un producto pensando en su manipulación, transporte y almacenaje
It could even be
relleno if you are referring to the padding that sometimes is added to protect cargo (the foam that sometimes we call "corchopan" in Spanish)
As you are probably at the top of the taxonomic tree, why not name it with the common function?
If the sub branches refer to material used to just fill the spaces, maybe «relleno» can fit.
«Protección», «acolchado» or «amortiguación» if the case is to avoid damage or even (specially the latter two) movement.
If the taxon is very broad and there are branches of everything, just «embalaje» should do, if there are no separate taxons dedicated to packaging in general.