Edge support is crucial in a mattress for several reasons. Firstly, you want to be able to sleep right up to the edge of a mattress without feeling like you’re going to fall out. Secondly, a robust edge allows you to sit on the edge of the bed. The third reason is one that you shouldn’t have to think about but is probably the most important: a good, robust edge increases the overall support in the mattress and will ensure a consistent feel across the entire face of the mattress.
There are a few different methods to add edge support in a mattress, we list the pro’s and con’s of each.
Steel perimeter frames
These are essential in any innerspring mattress to keep the springs together. They also add a nice, responsive level of support around the edge of a mattress. The frames consist of heavy duty (at least 5-6mm thick gauge), one-piece wire borders constructed with high-carbon steel that run around the top and bottom of a spring unit. The frames will ‘give’ slightly as you sit on the bed so you don’t feel an uncomfortable, hard edge under your legs.
The steel border wires are attached to every outer spring around the perimeter of the unit and the alloy will be tempered so the frames will last much longer than the normal lifespan of a mattress.
Butterfly Side Supports
These are used commonly by manufacturers when the steel perimeter frames around a spring unit are too light in wire gauge to offer enough edge support. The manufacturer will place them around the border of the spring unit to prop the sides up and weld them to the perimeter frames. This is not a construction technique that we recommend as you will be able to feel the supports wherever they are placed when you sit on the edge of a mattress. It’s far better to simply use a heavier wire gauge for the perimeter frames.
Occasionally, manufacturers use pillars or beams of polystyrene foam in place of these butterfly supports. This is even worse for a sitting edge as the pillars ‘give’ much less than a butterfly side support and are quite uncomfortable to sit on!
Foam Box Encasement
A firm foam edge is the only way to add edge support in a foam core mattress but manufacturers also use these as edge support around an innerspring mattress. The foam needs to be quite firm and a very high grade so that it outlasts the life of the mattress. Unfortunately, since a high-quality foam box can be the most expensive component in a mattress (costing even more than the spring unit), manufacturers will often use a lower grade of foam. As discussed in our articles about foam, this can mean that the foam encasement will wear out before the rest of the mattress components, rendering itself useless.
However, if the foam box is a very high grade and used around a ‘tied’ innerspring unit (such as bonnell spring), this can cut down on the lateral movement of the spring unit dramatically. The foam walls need to be thick enough to absorb the motion in the spring unit and can help considerably with partner disturbance in a mattress.
Unicase Foam Surround
Used in a well-known brand in Australia and marketed as the “unicase” edge support system, this is a form of polystyrene foam moulded into walls that encase an Offset coil spring unit. Whilst being considerably more durable than a foam box encasement, the unicase system does little to minimise partner disturbance in mattresses that use this style of edge support. This style of edge support is also extremely firm and only works with firm mattresses.