The type of equipment that a volcanologist would wear in the field depends on what they are doing.
Most of the time when they work on a volcano, they just wear a pair of heavy boots, jeans, hat, and long-sleeved shirt to protect from sharp dried lava.
They might use heavy work gloves if they are working on fresh lava flows and a rock-climbing helmet if working in an area where there is a lot of rock fall.
If needed they might wear a fire-retardant flight suit, a gas mask, or a flight helmet.
They might use one of the silver heat-resistant suits but it honestly does happen very rarely, most of the time these suits are too bulky and difficult to move around in to make them practical field gear.