What is the difference between mittens and trigger mittens?

Standard mittens have a single compartment for all four fingers plus a separate thumb. Trigger mittens add an articulated index finger compartment, allowing the index finger to separate from the other three fingers. This provides significantly better pole grip and basic dexterity while retaining most of the mitten's warmth. Trigger mittens are a popular choice for cold-weather skiers who need functional pole grip. The warmth difference between standard and trigger mittens is modest — trigger mittens are slightly cooler because the index finger is isolated, but the grip advantage is substantial.