<P> Structural aircraft - grade plywood is most commonly manufactured from African mahogany, spruce or birch veneers that are bonded together in a hot press over hardwood cores of basswood or poplar or from European Birch veneers throughout . Basswood is another type of aviation - grade plywood that is lighter and more flexible than mahogany and birch plywood but has slightly less structural strength . Aviation - grade plywood is manufactured to a number of specifications including those outlined since 1931 in the Germanischer Lloyd Rules for Surveying and Testing of Plywood for Aircraft and MIL - P - 607, the latter of which calls for shear testing after immersion in boiling water for three hours to verify the adhesive qualities between the plies and meets specifications . </P> <P> Usually faced with hardwood, including ash, oak, red oak, birch, maple, mahogany, Philippine mahogany (often called lauan, luan or meranti and having no relation to true mahogany), rosewood, teak and a large number of other hardwoods . </P> <P> Flexible plywood is designed for making curved parts, a practice which dates back to the 1850s in furniture making . </P> <P> Aircraft grade plywood, often Baltic birch, is made from 3 or more plies of birch, as thin as 1 / 64" thick in total, and is extremely strong and light . At 3 / 8" thick, mahogany 3 - ply "wiggle Board" or "Bendy Board" come in 4' x 8' sheets with a very thin cross grain central ply and two thicker exterior plies, either long grain on the sheet, or cross grain . Wiggle board is often glued together in two layers once it is formed into the desired curve, so that the final shape will be stiff and resist movement . Often, decorative wood veneers are added as a surface layer . </P>

When did plywood start being used in furniture