Resin is a crafting component in The Witcher 3: Wild Hunt that can be dismantled into sap. It is needed to craft the following items:
Crafting Requirements 
It can be found as random loot, guaranteed at some locations during the "Wine Wars" quest line in Toussaint, or purchased from the following merchants:
- All armorers and blacksmiths
- Armors and weapons merchants in Nilfgaardian Army Group 'Center' Camp
- Merchant in the boatyard south of Refugees' Camp
- Merchant at Calveit Watchtower
- Merchant at Coast of Wrecks
- Merchant in Ursten
- Merchant by the road west of White Eagle Fort
- Merchant at the sawmill northeast of Rannvaig
- Merchant at the Isolated Hut on Hindarsfjall
- Merchant in Mohrin Village
- Merchant in Stacheier
- Ducal Camerlengo in Beauclair
Resin can also be obtained by dismantling: