How contoured PORON shoe inserts work "like magic" to stop foot slide in high heels and flats, stabilize shoes and cushion the ball of the foot

January 02, 2019

I saw a review an Amazon customer wrote for the Ball of Foot cushions that I sell on Amazon. She said they were "like magic". Other customers have said things like, "I didn't expect these to work but they did!" One customer said, " I was not sure about buying these shoe inserts because they look so small, how would they cushion my foot enough? ". 

I was inspired by these comments from customers to create a pictorial explanation of how the shoe inserts work to do the several thing they do to make shoes - flats or heels -  comfortable. 

A key characteristic of the shoe inserts are that they are made from PORON, which is an open cell  polyurethane foam that never flattens no matter how many times it is stepped on inside a shoe. It springs back faster than the naked eye can see. This rapid speed of rebound means that the foam will rebound back up to its full height between each step. When the spring of the foam is restored between each step it can cushion each footfall with the same comfort.  There is only one other shoe cushioning product sold for high heels that uses PORON. This is the 'Foot Petals' brand. Their ball of foot cushions and full length shoe insoles are made from flat sheets of PORON foam which can only act to cushion vertical pressure. Contoured PORON foam can act to cushion vertical pressure, resist horizontal pressure and stabilize the foot. Closed cell foam, such as memory foam made into shoe cushioning is only helpful for adding comfort until it flattens and becomes hard with no rebound. Gel shoe inserts have a very small amount of rebound but will feel hard underfoot especially after a long period of wear.  

Killer Heels Comfort high heel inserts and ball of foot cushions are made from contoured PORON foam that is shaped to fit the underside of the foot. The shaped foam forefoot piece (ball of foot cushion piece) has a 6 mm (1/4")  high toe grip that is fitted into a hollow under the three middle toes and a 4.5 mm domed cushion that fits under the ball of the foot centered on the underside of the middle metatarsal.

The forefoot cushion or ball of foot cushion is a one piece forefoot cushion that can be worn in flats or high heels. For additional comfort in high heels a second PORON cushion that fits into the arch at the front of the heel can be added to keep the heel of the foot in place inside the heel of the shoe.  The ball of foot cushion with its' toe grip also helps keep the heel of the foot at the heel end of the shoe by stopping the entire foot from sliding forward.

The material of the shoe cushion being PORON is very important for its' function in two ways. PORON rebounds upwards so it cushions the ball of the foot at each step with a fresh springy cushion plus PORON rebounds laterally so it stops the foot from sliding forwards because the toe grip maintains its shape and returns to its full height of 6 mm immediately after each step.

At each step the foot moves forward a small amount inside shoes. This happens in all shoe although it is most obvious in high heels which puts the foot on a sloped ramp where it slides forwards easily even while the wearer is standing still. If the toe grip was made from a foam such as 'memory foam' it would indent a small amount at each step and begin to flatten from the ball of foot side until it flattened entirely. At that point the foot would override the flattened foam piece and it would no longer be effective in stopping the forward slide of the foot. 

Foot comfort results from the combination of the material of the shoe cushion being PORON so it never crushes, the PORON material shaped into a raised toe grip that stops forward slide of the foot and the dynamics of the different parts of the shoe cushion. Additional foot comfort is due to the tapered front end of the shoe cushion design that preserves normal toes functions of propulsion and balance. It is easier and less tiring to walk in any style of shoes, especially high heels, if the big toe can push against the insole of the shoe to propel the foot and the little toe can push against the insole of the shoe to balance the foot.  

The shoe cushion is dynamic in that it is in a constant cycle of compression and rebound with each footfall and foot lift. When cushioning material under the ball of the foot compresses it does so at the exact moment that the foot begins to slide forward. The simultaneous compression of the material under the foot and the intact state of most of the toe grip at a height of 6 mm allows the toe grip to stop the foot from moving forward because of its relative height differential of 4.5 mm above the adjacent compressed material under the foot. When the foot is lifted up the height differential between the cushioning under the ball of the foot and the cushioning under the toes (the toe grip) is only 1.5 mm which would be too slight to stop the foot from sliding forwards. 

  It is because of the rebounding PORON material and the sculpted design of the inserts that makes it  possible for a tiny shoe insert that is 2.5" long and 1/4" high to keep back the weight of a person from sliding forward inside their shoes - even in high heels- cushion the ball of the foot under its' maximum pressure point and stabilize the foot inside a shoe to prevent wobbling and keep the heel of the foot in place. 

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