Vertical desiccants are installed in container lashing rings and are designed to occupy minimal space in the container as they either fit into the container wall or are close to the container ceiling.
Horizontal desiccants are placed on top of the cargo (e.g. a pallet). A horizontally installed desiccant outperforms its vertical equivalent as the absorption is higher per kg desiccant installed. Further, the CO2 footprint is minimized as no accessories are needed.
Gel: The absorbed moisture is bound into a gel and thereby prevents leakage. In turn, it means there isn't any concern for the liquid, also says that vertical desiccants can be used horizontally.