October 5, 2023
Do Insoles matter in footwear? Many footwear brands select the insoles that go into a shoe last. Or they reduce the quality of the insole to save money before a new shoe hits the market. This approach is one of the WORST things you can do for comfort. Let's go over the science behind using insoles to make better shoes.
There is so much data on insoles to share that we're splitting the information into 3 parts:
Cushioning is one of Heeluxe's "Four Keys to Comfort". Insoles have a profound impact on how your customers perceive cushioning because they are so close to their foot. Often lab testing shows that people feel more cushioning from the insole than the midsole, even though the midsole is 4-6x thicker.
There are 3 ways that Heeluxe quantifies the cushioning benefits of insoles:
Perception testing. Our 7-point questionnaire shows that insoles increase comfort scores by 13.6% and perceived cushioning scores by 9.5%.
(Plantar) Pressure Testing. Using wireless pressure sensors while a person performs an activity in a shoe quantifies what they are feeling. These activities vary from walking in high heels to running to standing all day on a hospital work shift. Tests show insoles reduce pressure (aka improve cushioning) by 13.8% in walking shoes, 17.6% in running shoes, and 8% in high heels.
Hulk Impact Testing: this testing is an ideal way to analyze the performance of the foam used in an insole. The best performing insoles have 45% better cushioning performance than the worst insoles on this testing. Our testing adheres the the ASTM standards for 3Kj testing.
It's easy for an insole to provide good comfort when a customer first tries on a shoe. However, most insoles don't provide long lasting cushioning. In fact, some insoles lose all of their cushioning performance in just a few days of use!
Using Heeluxe's database of insole durability and cushioning performance, we see that insoles with premium materials maintain their cushioning 3-4x longer than lower quality insoles. What does that mean for your customers? They'll walk over 380 more miles in a premium insole before noticing the cushioning breakdown.
What makes a premium insole? The first key is the material. ETPU and LDPU are consistently the longest lasting materials in our insole database. The second key is the molding process. Die cut insoles tend to break down faster than compression molded insoles. We'll cover this in greater detail in part 2 of our insole science series.
Our standard for insole breakdown is 15% cushioning loss. This amount of cushioning loss is what an average consumer will perceive as a "dead" insole.
The influence of insoles on fit is obvious to most product developers: they know the insole allowance on the lasts they're using on a shoe. What most brands fail to consider is how a compressed insole will alter the fit of their shoe.
Over the first 150 miles of running an insole will compress on average 1.23mm (range 0.05-5.1mm). This compression of the insole loosens the fit by 1/4 size. When an insole compresses more than 3mm the fit in the width of the shoe will be 1/2 size looser. This change in fit is not optimal for our customers that liked the fit of the shoe when they purchased it!
Many brands we speak to believe that the change in fit of a shoe is due to the upper material "breaking in" or stretching out slightly. This is true only in shoes that are made with stiffer natural materials like leather or canvas. Many modern shoes made out of knits, wovens, and synthetic materials become looser over time due to insole compression.
Insoles have a massive impact on comfort, cushioning, durability, and fit of a shoe. Now that you're excited about the power of insoles, please read our second post about the features of the best performing insoles.
If you have questions about testing your current insoles please contact firstname.lastname@example.org.