The coils, also known as the core or the
innerspring unit, provide
the main support for the body. Proper support is essential not only
for a good night's sleep, but for maintaining a healthy spine. When
considering the core of an innerspring mattress, there are a number of
important factors: the number of coils used throughout the mattress, the
way the coils are constructed, and the shape of the coils.
You might have heard a rumor
that the more coils in a mattress core, the more supportive the mattress
will be. While this can be true,
coil count is not nearly as critical today as it once was. These
days the construction of the coils is a much more important factor in determining
the overall comfort and support of the mattress. That being said, here
are some guidelines to follow vis-à-vis coil count:
typical mattress contains between 250 and 1,000 coil springs
mattress with a lower coil count might use thicker wire or other techniques
to compensate for this (see Coil Construction below)
As a rule
of thumb, the minimum number of coils you should look for in a mattress
is 300 for a full, 375 for a
queen and 450 for a
When discussing the coils of an innerspring mattress,
the word "gauge" refers
to the thickness of the wire used to construct the coil. Somewhat
counter-intuitively, the lower the number, the "heavier" the
gauge, and the thicker the wire — 12.5 gauge wire (very "stiff")
is thicker and stronger than 16.5 gauge wire (quite "springy").
Another important factor is the number
turns" in each
coil, a measurement of how tightly the coil is wound. Coils constructed
with a higher number of working turns will result in both a softer and
more durable mattress,
since the work of supporting your body is spread throughout the spring.
Working turns can be counted by tracing the wire with your finger — each
time your finger travels 180 degrees around the coil translates to one
the process of heating and cooling the coils to ensure they retain their
proper shape over time. A "double
heat tempered" coil
has gone through that process twice, ensuring increased durability.
Hourglass coils, the most commonly used design,
come in two varieties — Bonnell
coils and Offset coils. Based on 19th century buggy seat springs,
the Bonnell coil has an hourglass shape with a knot at each end, and is
known as the original mattress coil. Today, Bonnell coils are still
the most prevalent coils in the mattress industry, though they are typically
found in less expensive mattresses. The Offset design, found in
more expensive mattresses, is similarly hourglass shaped, but the circles
at the top and bottom of each coil are flattened to create a hinging action
within the mattress core. This design allows the mattress to better
conform to your body, and tends to make Offset coils less noisy than their
Bonnell predecessors. It also allows Offset coils to be connected
to each other via helicals (corkscrew-shaped wires that run over the tops
and bottoms of the coils), which prevents them from moving from side to
side when compressed.
Pocketed coils, also known as Marshall coils,
are each individually wrapped in a fabric pocket. While the pockets might
be connected together, the springs are each independent of one another
and can move separately. Pocketed coils provide more motion separation
than other innerspring coil types, meaning that when your sweetie starts
tossing and turning, you are less likely to be disrupted from your zzz's.
This can really come in handy if your bed-mate is a restless sleeper. On
the flip side, pocketed coils endure greater strain over time, since each
coil absorbs weight without distributing it to other nearby coils. Simmons uses
pocketed coils in most of their innerspring mattresses.
Continuous coil springs are made from a
single length of wire shaped into a series of loose S-shaped ringlets.
The concept behind this design is that by attaching each coil to its neighbors,
the mattress core will be stronger, more stable, and more durable. Continuous
coil designs also allow for significantly more coils per mattress, making
it difficult to compare coil counts with non-continuous coil systems. Both
Kingsdown tend to use continuous coils in their products.