A unique design feature, sprung and belted seats are used to increase comfort and can be found on many of our fixed height wooden bar stools and dining chairs. A framework of elasticated belts and springs is incorporated beneath the seat padding to provide excellent support. The arrangement of the springs and belts may differ depending on the design, with some only using belts, but they all offer a luxurious seating experience

- https://www.atlanticshopping.co.uk/furniture-glossary-of-ter...

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Not only are these chairs strong and sturdy they also provide the ultimate comfort with their spring and belt seat construction and medium density foam padding. - https://www.amazon.co.uk/OAK-FURNITURE-KING-Oregon-Leather/d...

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During all past years these chairs were restored many times: the soft material is changed and no one knows that the original look was like, what is more, the wood is painted to different color then natural wood texture. As my grandmother told, springs and belts at the bottom of the seat may be original. - https://www.myantiquefurniturecollection.com/age-and-style-o...

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The internal steel structure features springs and elastic belts for guaranteed comfort and durability. - http://www.thebuildingsource.com/product/24502/sitland-path-...