A PFD (Personal Flotation Device) is a wearable safety vest or garment designed to keep a sailor afloat in water, ranging from comfortable buoyancy aids for active sailing to high-flotation life jackets. Unlike traditional life jackets, PFDs are designed for all-day comfort and mobility, making them common in, for example, dinghy sailing.

Key PFD Concepts & Types
Buoyancy Aids (Level 50): Common for dinghy sailing and water sports, these allow good mobility but require the wearer to be a conscious, competent swimmer.

Life Jackets (Level 100+): Provide higher buoyancy and can turn an unconscious person face-up.

Inflatable PFDs: Use CO2 cylinders, either manually pulled or automatically activated by water pressure, to provide high buoyancy.

Usage Scenarios: PFDs should be worn in bad weather, at night, by children, by weak swimmers, or when sailing alone.

Key Differences
PFD vs. Life Jacket: While often used interchangeably, a PFD is typically more comfortable, while a life jacket is specifically designed to float a person face-up.

Safety Essential: They are often required by law to be worn on small vessels, such as those under 7m in some regions, or on deck at all times for children.

PFDs are not just limited to vests; they also include throwable devices like rings.