Toe protection: Steel or composite toe caps provide protection against falling objects and compression. Composite toes are lighter and don't conduct electricity or extreme temperatures as much as steel.
Slip resistance: Look for SRC-rated soles for the best grip, or boots that meet ASTM safety standards for slip resistance.
Puncture resistance: A midsole, either steel or non-metallic, can protect against sharp objects on the ground.
Electrical hazard (EH) and static dissipative (ESD): These are important for specific environments. EH boots protect against accidental contact with live electrical circuits, while ESD boots help control electrical discharge from the body.
Water resistance/waterproofing: Essential for working in wet conditions to keep feet dry.