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  • Why Do Life Jackets Float?

    Why Do Life Jackets Float?
    Life jackets are a standard piece of safety gear for all boating activities, but how they work is sometimes poorly understood. Life jackets float because of the science of buoyancy and are designed to put that science to its best effect.


    The first principle behind why anything floats is density, or how much matter is crammed into a given volume of space. For example, lead is denser than iron because a lead ingot has more mass than an iron ingot of equal size and therefore weighs more.


    Objects are buoyant, or float, if they have an overall aggregate density that is less than that of water. For example, most forms of wood float despite being solid because wood fibers are packed with air pockets, lowering their density to less than that of water.

    Practical Buoyancy

    A life jacket needs enough buoyancy to compensate for a human body and water-logged clothing that will increase its aggregate density when used.

    Life Jacket Design

    Life jackets have two basic designs that achieve buoyancy differently: the foam core life jacket and the air bladder life jacket. Both are made so that, if left undamaged, they will not become water-logged and lose buoyancy.

    Foam Core

    The exact foams used in life jackets can vary, but the one thing they have in common is that they are honeycombed with air pockets in the same way wood is. A solid block of the plastics used to make the foam blocks in life preservers would sink on its own, but because the foam blocks are made with many air bubbles they have an overall density that is much lower than that of water.

    Air Bladders

    Another common design for life jackets is to arrange one or more air bladders that are automatically inflated using a carbon dioxide capsule. These may or may not have a manual inflation hose as well.

    Article Written By Edwin Thomas

    Edwin Thomas has been writing since 1997. His work has appeared in various online publications, including The Black Table, Proboxing-Fans and others. A travel blogger, editor and writer, Thomas has traveled from Argentina to Vietnam in pursuit of stories. He holds a Master of Arts in international affairs from American University.

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