A process for producing a preform by cold spray deposition, the process comprising: providing a starter substrate about a preform axis of rotation, the starter substrate having at least one axial end having a substantially flat deposition surface; rotating the starter substrate about the preform axis of rotation; depositing material onto the deposition surface of the starter substrate using cold spray deposition to form a product deposition surface, the cold spray deposition process including a cold spray applicator through which the material is sprayed onto the deposition surface; successively depositing material onto a respective top product deposition surface using cold spray deposition to form successive deposition layers of the material; and moving at least one of: the cold spray applicator; or the starter substrate and preform product, relative to the other in an axial direction along the preform axis of rotation to maintain a constant distance between the cold spray applicator and the top product deposition surface, thereby forming a preform product of a selected length, characterised in that the cold spray applicator is moved in a plane perpendicular to the preform axis of rotation so as to deposit material as a substantially flat surface on each respective deposition surface of the starter substrate or product deposition surface of the preform product, the flat surface of deposit material being maintained through controlled movement of cold spray applicator, and wherein movement of the cold spray applicator is controlled so that the instantaneous velocity of the cold spray applicator relative to the deposit surface is inversely proportional to radial distance the cold spray applicator is to the preform axis of rotation. providing a starter substrate about a preform axis of rotation, the starter substrate having at least one axial end having a substantially flat deposition surface; rotating the starter substrate about the preform axis of rotation; depositing material onto the deposition surface of the starter substrate using cold spray deposition to form a product deposition surface, the cold spray deposition process including a cold spray applicator through which the material is sprayed onto the deposition surface; successively depositing material onto a respective top product deposition surface using cold spray deposition to form successive deposition layers of the material; and moving at least one of: the cold spray applicator; or the starter substrate and preform product, relative to the other in an axial direction along the preform axis of rotation to maintain a constant distance between the cold spray applicator and the top product deposition surface, thereby forming a preform product of a selected length, characterised in that the cold spray applicator is moved in a plane perpendicular to the preform axis of rotation so as to deposit material as a substantially flat surface on each respective deposition surface of the starter substrate or product deposition surface of the preform product, the flat surface of deposit material being maintained through controlled movement of cold spray applicator, and wherein movement of the cold spray applicator is controlled so that the instantaneous velocity of the cold spray applicator relative to the deposit surface is inversely proportional to radial distance the cold spray applicator is to the preform axis of rotation.