Comfortable and Beautiful Furniture Design
Furniture design falls into two basic categories: visual and functional. Foam can affect both.
Since the visual aesthetic of furniture design is virtually unlimited, and foams can be fabricated or molded to meet any of a variety of requirements, it is important to include functional considerations when developing the furniture.
Functional design should take into account a number of factors, all of which may work with each other, assisting in providing the correct degree of seating comfort. Fabric type, spring type/design/construction, seat/back geometry, basic frame design, physical events during actual sitting/leaning, seating foam type, construction of the back, and firmness ratio between seat and back are major design factors to be considered in seating and comfort design.
Specifying Foam for Upholstery Applications
A number of foam properties will affect design considerations and is important in developing upholstery that provides proper comfort.
DENSITY: Affects the foam’s ability to provide support, comfort and durability. Generally speaking, as foam density increases, durability also increases. Some of the factors related to durability are loss of firmness (flex fatigue), breakdown in the sitting area of the cushion (dishing), and fabric bagging caused by loss of foam dimensions (compression set). Choosing the proper foam density will reduce the impact of these over time.
IFD: A measure of foam firmness that is independent of density. Even high density foams can be soft. For upholstery, 25 percent IFD can range from five pounds to 50 pounds. Softer foams may be laminated to firmer foams to provide surface softness. Firmness can affect the “ride” of a cushion. The ride is the distance that a weight will travel while still being comfortable. Firm foams are often used to create certain “feels” as in thin- profile applications such as in arms or backs. Firm foams are often used to create or hold certain shapes.
COMPRESSION MODULUS (SUPPORT FACTOR): Compression modulus is generally a function of the type of foam. Conventional foams have compression modulus in the range of 1.9 to 2.1; filled foams 2.1 to 2.4; and high resilience grades 2.2 to 3.0. Within a foam grade, the modulus is a function of the foam density. The higher the density the greater the compression modulus. Laminating hard and soft foams together can also increase compression modulus for the composite cushion structure. However, the firmness of the laminated foams cannot be too far apart or the cushion may seem to “bottom out” on the firmer portion.
Compression modulus affects cradling. For greatest comfort, the compression modulus should be selected to maximize cradling. When cushions are thick, lower compression modulus foams may be used to improve cradling and to achieve more even distribution of body weight. If cushions are thin, not too much TVM can be expected. Interfacial pressures of these designs will definitely decrease the comfort of thin cushion seating systems. Higher compression modulus foams may be used in thin cushion applications to prevent system “bottoming” and/or “hammocking” of the seating area.
FLEX FATIGUE: This important measurement of durability is an indicator of a cushion’s long term ability to provide the proper cradling and TVM. Foams that have good flex fatigue values will tend to retain their original firmness and support levels, which means that the cushion can retain more of its original characteristics.
RESILIENCE: The surface resilience of a foam also affects comfort and design. Foams with high resilience
feel springy and provide a good “hand” for cushioning. Conversely, low resilience, or a “dead” feel, typical of many viscoelastic (memory) foams, may be desirable in some pillow and padding applications.
Like design aesthetics, functional designs can vary tremendously, and designers can create comfortable seating by varying design considerations. Ultimately, the intended use for the furniture must dictate much of the design.
