20 Pounds Sterling

Clydesdale Bank's polymer £20 was issued as part of a broader industry-wide transition away from cotton-fibre paper that Scottish commercial banks undertook largely in step with Bank of England timelines, though Scottish issuers retain the legal right to produce their own notes under longstanding arrangements dating to the 1845 Bank Notes (Scotland) Act. De La Rue had been producing Scottish commercial banknotes for decades before the polymer switch, and the move to Guardian substrate brought the Clydesdale series into alignment with security standards that paper simply couldn't match.

Colour-shifting ink on polymer behaves differently than on paper — the optical effect is sharper and more reliable across a wider range of lighting conditions, which was one of the practical arguments for the transition beyond counterfeiting resistance alone.