A plastic flask is a lightweight, durable, often shatterproof container, typically made from materials like polypropylene (PP) or polycarbonate (PC), used in labs for mixing, heating, and storing liquids, featuring a conical or round shape with a narrow neck for easy swirling and spill prevention, often with clear volume markings and screw caps for secure closure, serving as a safer, cheaper alternative to glass, though less efficient for precise insulation than vacuum flasks.