While Wolverine is the poster child for superhuman healing factors, he isn't the only hero with the ability, and Namor boasts a unique way of healing himself. Unlike the more well-known heroes who heal at an advanced rate, the King of the Sea's ability is perfectly constructed to fit his character's story and background. These differences help distinguish the power, allowing Namor to keep fighting without making him indestructible.
Wolverine's healing factor is incredibly powerful and has helped him stay alive through otherwise fatal wounds. He's grown full limbs and his body back before, and his life in general is extended to the point of immortality. Namor is similarly long-lived, but he can't rely on his body to survive any injury like the X-Men's resident brawler.
This power of Namor's is actually shared among the Atlantean people, who heal skin tissue when they are in water. However, because of his mutation and the circumstances of his birth, Namor's healing factor is faster compared to his people's, and much stronger. Of course, it can't accomplish feats on the same level of growing back half his body, but it still gives him time to recover from fights, as he'll retreat to water afterwards to close any wounds and regain energy. This power was most effective during WWII, when Namor would tear through Nazi ships like a torpedo, but it's still effective in the modern day, as it means that Namor is back up and swinging shortly after even the most devastating fight. In many ways, Namor's healing is more intriguing than Wolverine's, as it allows him to survive otherwise life-ending damage, but only if he's able to walk away from a given fight.
Namor's Healing Factor Activates in Water
One such instance of literally saving Namor's life was in Thunderbolts (1997) #165 by Jeff Parker, Kev Walker, Terry Pallot, Chris Sotomayor, and Joe Caramagna. After an intense battle, Namor was struck down and had to be saved by placing him in a bath and performing a spell that would make his body believe he'd been in Atlantean waters for a month. This jumpstarted the healing process and by the end of it, he was back to full strength. The regenerative ability gave Namor the element of surprise, as his foes believed him to be struck down, but because people very rarely think of his ability, he has an upper-hand in a lot of fights. One downside is that the dryer he becomes, the slower he heals, and if he is completely dry he won't have any form of accelerated healing, and can even be weakened below his superhuman potential.
Namor does have one injury that his healing factor can't fix. Because the wings on his feet are the result of a mutation, they remain unaffected by the healing factor that his Atlantean blood gives him, and his wings can only heal naturally and very slowly, even when in water. While many think of Namor as a purely water-based hero, his enhanced strength, durability, and flight make him a powerhouse fighter - one who has staggering stamina and healing so long as he's able to return to the sea when needed.
As Atlantis' Avenging Son, Namor picks the fights no-one else will, and despite being just as ferocious as Wolverine, his healing factor only guarantees that he must keep fighting again and again, even though it can't save him from a truly fatal injury.