IMPAK Foam is the protective material built into the ankle zones of TENTEN’s socks, and what makes it different from a standard foam pad is that it is non-Newtonian. In its resting state it is soft, only 3mm thick, and flexible enough that you barely notice it is there. The moment an impact occurs, the material’s structure changes almost instantly, becoming far more resistant to the force passing through it, before returning to its original soft state just as quickly. Below, we explain what “non-Newtonian” actually means, and share the impact test data behind TENTEN’s headline claim that IMPAK Foam absorbs up to 65% of impact force.
What Does “Non-Newtonian” Actually Mean?
Most everyday materials are Newtonian, meaning they respond to force in a simple, predictable way. Water stays runny whether you stir it gently or violently. Non-Newtonian materials break that rule: their resistance to force changes depending on how much force is applied. The classic kitchen table example is a mixture of cornflour and water. Stir it slowly and it behaves like a liquid. Hit it or squeeze it quickly and it briefly behaves like a solid. That instant change in behaviour under sudden force is called shear thickening, and it is the same underlying principle behind a number of modern protective materials used in motorsport suits, ski back protectors and body armour, where the goal is something that stays soft and flexible for everyday movement but stiffens instantly to absorb a sudden impact.
Why Build It Into a Sock Instead of a Separate Guard?
Traditional ankle protection, rigid braces or strapped on guards, works by physically limiting how far the joint can move. That is effective, but it is also bulky, needs fitting every session, and can restrict the kind of natural movement footballers, rugby players and basketball players rely on. Building a 3mm non-Newtonian pad directly into an anatomically shaped compression sock takes a different approach: nothing extra to put on, nothing that changes how your boot fits, and protection that is simply already there whenever you play.
How the 65% Figure Was Tested
TENTEN’s foam pads are tested using the EN 1621-1:2012 impact test method, a European mechanical impact protocol originally developed for certifying limb protectors in motorcycle clothing, and widely used across the protective equipment industry as a benchmark for how well a padded material spreads and absorbs a sudden impact. The test works by dropping a fixed weight onto a sample from a set height, at a set temperature (here, 23 degrees Celsius), and measuring how much force passes through to the surface underneath. A lower force reading means more of the impact energy was absorbed by the material rather than transmitted through it.
Two impact energies were tested, a lower-energy 5 joule impact and a higher-energy 10 joule impact, each compared against a bare sock with no foam pad fitted, as a baseline. Here is what the testing found:
| Impact Energy | Bare Sock (mean peak force) | Sock + 3mm Foam (mean peak force) | Force Reduction |
|---|---|---|---|
| 5 J (lower-energy impact) | 19.14 kN | 9.29 kN | 51.45% |
| 10 J (higher-energy impact) | 44.70 kN | 15.67 kN | 64.94% |
At the higher 10 joule impact energy, closer to the kind of forceful direct knock a player might take from a stud or a collision, peak force dropped from a mean of 44.70 kN with a bare sock to 15.67 kN with the 3mm IMPAK Foam pad fitted, a 64.94% reduction. That is where TENTEN’s “absorbs up to 65% impact force” claim comes from: it is the reduction seen at the higher, more forceful end of the tested range, not a fixed number. At the lower 5 joule impact energy, the reduction was 51.45%, which is still a substantial cut in the force reaching the ankle, but meaningfully lower, which is exactly why the claim is phrased as “up to” 65% rather than a flat 65% across every kind of knock.
The foam sheet tested was 3mm thick, with a density of 0.350 g/cm³ and a hardness of 25 on the Shore hardness scale used for foams of this kind, matching the specification used in TENTEN’s finished socks. This is manufacturer testing carried out to the EN 1621-1:2012 method, not a substitute for accredited third-party certification.
What This Means in Practice
No sock, brace or piece of protective equipment can prevent every injury, and IMPAK Foam is not a substitute for good technique, proper warm up or appropriate footwear (see our guide to preventing ankle sprains in football for the full picture). What this data shows is that the 3mm foam pad meaningfully reduces the peak force reaching the ankle in a standardised impact test, roughly halving it at a lower impact energy and cutting it by close to two thirds at a higher one, which is the mechanism behind the protection TENTEN socks are built to provide.
Who This Technology Is Built For
IMPAK Foam is aimed at core contact and change of direction sports, football, rugby and basketball in particular, where there is a genuine, repeated chance of taking a knock to the ankle. It is built for players who want protection without giving up the feel of a normal sock, rather than as a replacement for medical grade bracing during active rehab from a significant injury.
You can see the full technology breakdown and this same test data on our Technical page, or browse the current range in the Shop.
Written by the TENTEN Protection team.
