How mattresses are made
Traditionally, a mattress is built from the spring unit up, with many parts of the process still completed by hand. In very large, high-tech mattress factories, only the heavy lifting of the mattresses between process areas has been automised and all other tasks, such as applying the foams or stitching the fabric layers to the mattress, is still done by craftsmen’s hands.
A spring unit, whether it be a traditional Bonnell or a more premium pocket spring, will usually be purchased from a spring manufacturer as one piece. Even when the springs are manufactured overseas, (as most spring units used in Australia are) where they are shipped compressed in containers, the units only need to be opened and have side supports applied around the perimeter of the unit.
These side supports consist of solid steel border frames that are welded or joined with solid rings in multiple points around the top and bottom of the springs. If the border frames are not robust, then other side supports such as butterfly-shaped metal pieces are added at intervals around the sides of the unit.
It is common for manufacturers to then place the spring unit into a foam encasement, commonly called a foam box. Whilst this can help to reduce the movement in a mattress spring unit, it is not a good practice to use these foam boxes to increase the side support. Foam will break down many years before a spring unit so the walls of the foam box can dip or bow out to the side as a mattress ages.
The construction process begins when the spring unit is placed on a high table or conveyor belt ready for the upholstery layers to be built around the unit. The entire construction time from here until the mattress is bagged can be as little as 20 minutes. Of course, more premium style mattresses will take longer as more care is taken with the stitching and application of the foams.
The first layer of upholstery over the springs will be an insulation layer. This is usually thick felt, manufactured with recycled rags and other synthetic or natural fibres. The insulation layer’s primary job is to prevent the foams and fillings from sinking into the spring unit and to protect the fragile foams from having any contact with the metal springs. This felt layer will be attached over the spring unit with solid metal rings, known as hog rings. These rings are applied with a high-pressure gun that fastens the ring through the felt and around one of the outer springs.
Next will come the base layer of foam, usually the firmest layer of all the foams used in the comfort layers. Following this will be the final layers of foams, finishing with the most premium foams such as latex or memory foam. A well-constructed mattress will always have these premium foams as close to the top of the mattress as possible so that the sleeper will be able to utilise the pressure-relieving properties of these foams.
Foam layers are glued with a glue mixture that bonds the foams without causing them to erode. This glue is often a mix of natural rubbers and synthetics. Fixing these foam layers together is an essential step in mattress construction, for without this, the layers will undoubtably shift whenever the sleeper turns or moves on the mattress.
Some bed-in-a-box companies espouse the use of foam layers that can be changed or turned over by the consumer. This sounds like a good idea, but you should be aware of the potential discomfort that you will feel in these beds when the foams start to move, bunch and fold over each other. I wouldn’t be too happy to have to constantly open up the mattress to adjust these foam layers.
Once all of the comfort layers have been applied over the spring unit, a pre-cut border of upholstery-grade fabric will be wrapped around the sides of the mattress and sewn into place.
The mattress quilt is then applied. This will be a one piece layer that has been pre-sewn to the exact size of the mattress. This panel consists of the top mattress fabric, fillings of cotton, polyester, wool or foam and an underside fabric, with all layers sewn together by a huge quilting machine.
The quilt panel, upper foam layers and mattress border fabric will then be sewn together using a wide fabric tape or ribbon. Even this last process will commonly be done by hand, with the worker pushing the entire mattress through a sewing machine known as a tape edging machine. It is quite a skill to be able to achieve a nice straight line as this ribbon stitches together the outer layers of the mattress.
The mattress is then flipped and another layer of insulation felt will be attached to the underside of the spring unit and joined to the springs with hog rings.
Finally, an underside panel of fabric is sewn together with more fabric tape to join the border fabric.
Before being placed into a mattress bag, the finished product is assessed by a quality-control worker who will check the overall construction and stitching and trim any loose threads left over from the quilting and tape edging machines.