The incorporation of inorganic nanofillers into polymeric matrices represents an effective strategy for the development of smart coatings for corrosion protection of metallic substrates. In this work, wet-jet milling (WJM) exfoliation was used to massively produce few-layer hexagonal boron nitride (h-BN) flakes as corrosion-protection pigment in polyisobutylene (PIB)-based composite coatings for marine applications. This approach represents an innovative advance in the application of two-dimensional (2D) material-based composites as corrosion protection systems at the industrial scale. Although rarely used as an organic coating, PIB was selected as a ground-breaking polymeric matrix for our h-BN-based composite coating thanks to its excellent barrier properties. The optimization of the coating indicates that 5 wt.% is the most effective h-BN content, yielding a corrosion rate of the protected structural steel as low as 7.4 × 10-6 mm year-1. The 2D morphology and hydrophobicity of the h-BN flakes, together with the capability of PIB to act as a moisture barrier, are the main reasons behind the excellent anticorrosion performance of our composite coating.