Which permeability shall I use?

Low permeability is better suited for whites and those red varieties with low tannic and phenolic content (often Grenache responds better to LP).

Medium permeability is the most versatile option, works very well with most Cabernets, Shiraz, Pinotage, Pinot Noir, Carmenere and Merlot.

High permeability ideal for varieties with high tannic and phenolic content where a softer finish or earlier release is beneficial (Petite Syrah will often respond better in HP)