Diagram: Heavy leather jacket is a crafting diagram in The Witcher 2: Assassins of Kings that is needed to craft a Heavy leather jacket.
It can be purchased from Sendler during Chapter I, and Mael during Chapter II.
Diagram can also be taken as a reward from family members of the people you saved in the "Woe to the Vanquished" quest. (You shouldn't ask for money from them in Prologue.)