The posture box is a wooden frame with a flat top, covered with the same ticking as the mattress. This type of construction is usually the least expensive, made of pine or a similar hardwood, covered with some type of particle board. The posture box has no springs and does not work well to absorb the weight from the mattress. A mattress on a posture box will most likely have a shorter lifespan.
The semi-flex grid is a wooden frame with a rigid metal wire grid attached above 7 or 8 supporting slats. The semi-flex grid is firm and minimizes flex to support the mattress.
The foam foundation is made of a high density foam and is used to support foam mattresses. This foundation provides an even distribution of weight from the mattress, helping prolong the mattress life.
Coil Spring or Box Spring
This foundation features a heavy-duty spring coil system to support the mattress. If the springs match the mattress it is called a coil upon coil box spring. The coils are made of a heavy-gauge wire to help absorb impact to the mattress. The coil spring foundation provides good support and a softer feel than the more basic foundations but reasearch has shown that boxsprings move too much and cause some innerspring mattresses to sag prematurely. Most mattress manufacturers have switched to a rigid foundation (see Modular Grid below) making mattresses last longer. For more information on coils and guages, see Coils and Guages.
The modular grid or grid foundation, is considered by many to be the best support for a mattress and is used in the best quality sleep sets. Heavy-gauge square coils are attached to a wood frame, which tends to have more slats than less expensive foundations. The square coils evenly absorb the torsion of the weight transferred to them, and help prolong the life of the mattress effectively.
What type of support does a sleep set need? This is an important factor for larger bedding where improper support can result in twisting or sagging of the sleep set. The side rails of a bed frame provide adequate support for twin and double-size sleep sets but queen-size or king-size sleep sets require some extra support. Select a frame that has a center support rail with extra legs – six are preferable to the standard four. Make sure you understand the correct support required for your mattress set because inadequate support may invalidate your warranty.