Folded fin heat sinks are best when there is ducted air, that is, air flow is directed through a duct of some kind directly at the heat sink. Fin pitch can be optimized in the manufacturing process making this kind of heat sink, with ducted air flow, very high performing. Also, because the heat sink material is folded, there can be a big increase in surface area over which heat can be dissipated. Fold fin heat sinks have high heat flux density. The drawbacks to this type of heat sink are the cost including manufacturing and ducting necessary in your system.