Codex: Chaos (1996), p27 — The Marks of Chaos

Nurgle

Champions bearing the Mark of Nurgle are swollen with corruption, their armour barely containing their bloated bodies. Because their bodies are dulled with disease and partly rotted away they feel little pain and can endure considerable injury without discomfort. A Chaos Champion of Nurgle always adds an extra +1 to his Toughness on account of his hugely bloated body.