One of the main components of cooling towers is the packing which is made of lightweight plastic material. The packing or fill provides a heat transfer surface for evaporation without restricting the air flow.

A narrow channel spacing is more efficient with more heat transfer area per meter cube, however also more prone to fouling from airborne particles.

The choice between a narrow and wider channel spacing is a balance between efficiency and risk of blockage usually one would see airborne debris or biological growth on the packing.

Calcium carbonate or scale are less of a problem as the surface temperatures are the lowest in the loop and calcium carbonate remains dissolved at cold temperatures.