Fire is a hazard in the Pikmin series. Most Pikmin types are not resistant to fire, and if they touch a fire source, the top of their stems will begin to burn up, they will run around in a panicked state, and if not saved, will eventually succumb and die. They can be saved by being whistled at. Red Pikmin and Bulbmin are completely immune to fire, making them necessary to handle obstacles or enemies that can produce or are under fire.
Leaders are not normally invulnerable to fire hazards: they will take damage and be knocked back if they touch fire. However, by salvaging the Scorch Guard, they will be rendered completely immune to fire. However, they can still be damaged by the Titan Dweevil's Flare Cannon.
Some obstacles and enemies can generate flames, while others are constantly burning up.
The Scorch Guard is a spacesuit upgrade in Pikmin 2 and Pikmin 3. After is is collected, the playable leaders will gain immunity to all sorts of fire attacks, just like Red Pikmin. The exception is the Titan Dweevil's Flare Cannon, since it will stun leaders, even if it doesn't harm them.
Red Pikmin are resistant to fire, meaning they will not be affected by any flame and will act as if it does not exist. Bulbmin also share this trait. This makes them quite valuable when fighting against fire-related enemies and overcoming fiery obstacles. Unlike other Pikmin types that can resist a certain hazard, Red Pikmin cannot use fire to their own advantage, nor can they interact with it.
In the Super Smash Bros. series
Some fighters in the Super Smash Bros. series have attacks that can set their opponents on fire. Olimar is one of them – when a Red Pikmin attacks an enemy, it burns them. Similarly to the Pikmin series, Red Pikmin can completely resist any attack with a fire property, by taking no damage and not flinching.