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MANUFACTURING & MATERIALS INNOVATION
WF
28
T
he idea of designing footwear with comfort as the
primary aim really started with the sports shoe
phenomenon of the latter part of the last century.
Wearers found the shock absorbing qualities of these shoes
offered a new walking experience and began to demand the
same in their every day footwear. While the bulky nature of
sports shoe soles allowed for a substantial shock and
pressure absorbing layer to be incorporated, the thinner soles
of dress shoes did not, so another solution was needed. The
answer was a thin urethane foam developed by Rogers
Corporation in the U.S.A. during the 1970s called Poron
Performance Cushioning.
WHAT IS IT?
Poron is the name given to a series of flexible
polyurethane foams made from chemical reactions between
isocyanates and polyols. A mixture of these two chemicals is
mechanically frothed and spread on to a substrate. The
reaction between them is then accelerated by heat to turn it
into a fully cured foam sheet. While this may sound simple,
needless to say it is not. The reason Poron foams do what
they do lies in their structure, so the first thing is to consider
what is demanded of them.
In most instances, under-foot comfort depends mainly on
the insole or the foam foot bed material combined to it.
Modulus or softness in this area affects both immediate
(perceptive) and long-term (performance) comfort. End use
determines the required modulus so dress shoes tend to use
soft foam and sports shoes a much firmer one. A wide range
of modules is therefore essential.
Cell structure is all-important and uniformity of cell
formation essential. If it collapses under compression and
temperature, compression-set resistance and impact
attenuation can be greatly reduced. Furthermore, a non-
uniform cell structure can also lead to inconsistent moisture
management which is another facet of overall foot comfort.
Open cell foams perform better in thin substances than
closed ones which derive a significant proportion of their
PUTTING A BOUNCE
INTO WALKING