Stable materials remain inert, with little or no dimensional change, when changes occur in moisture, temperature, or applied force. MDF is one of the most dimensionally stable wood composite materials and is used as a substrate for veneers. Marine-grade plywood is excellent for outside or wet conditions. It is able to withstand submergence in boiling water for an hour without delaminating at the core. (Cassina uses marine plywood to manufacture Gerrit Rietveld’s Red-Blue chair.) Ceramics, granite, stone, and thermosetting plastics are stable materials unaffected by moisture and temperature. The epoxy resin 543 Broadway chairs designed by Gaetano Pesce are made from a thermosetting epoxy resin and are not affected by heat or daylight, as would a chair made from a thermoplastic (Figure 7.25). All materials creep—that is, deform over time when subjected to a constant load. This is evident when long, thin wood shelves gradually sag.
Particleboard is a composite wood product made with formaldehyde, which does not prohibit moisture from causing the wood chips to expand. This makes particleboard
particularly susceptible to structural deformation when exposed to moisture. For this reason, particleboard should not be used in furniture unless it is adequately supported.