An ink comprises (i) transition metal ion source, (ii) reducing agent, and (iii) polymer and/or polymer precursor with polymerisable terminal multiple bonds. The ink may contain 5-50 wt.% transition metal ion source, such as salts, oxides, or complexes, which may comprise silver or copper. The ink may include 1-10 wt.% reducing agent, optionally selected from formate, carbamate, carboxylate, hydrazinecarboxylate, or carbonates/bicarbonates of amines or ammonium. The polymer may be a thermoplastic or an elastomer, especially polyisoprene rubber, polydimethylsiloxane, or polyurethane. The polymer precursor may be (meth)acrylic acid or acrylamide. The ink preferably comprises 0.5-10 wt.% polymer/precursor. The transition metal ion source and polymer/precursor may be a single compound, e.g. silver acrylate. A method of manufacturing a deformable conductor comprises applying the ink to a deformable substrate and thermally treating or irradiating the ink. An electronic device, particularly a wearable or stretchable device, comprising the deformable conductor is also disclosed.