The E on a safety shoe stands for energy absorption of the seat region, which is the standard's term for the heel. It means one specific thing: in a laboratory, that heel absorbed at least 20 joules when it was compressed. That is the whole claim.
It is not a comfort rating, it is not a measure of how the shoe feels at hour nine, and it is not a score you can compare between two models, because a heel that absorbed 21 joules and one that absorbed 45 carry exactly the same letter. Understanding what the test actually does is the fastest way to stop over-reading the marking and start looking at the things that genuinely decide how a shoe feels underfoot.
What the E Marking Actually Certifies
Like antistatic performance, energy absorption is written into the base requirements of the main safety classes rather than sold as an extra. If your shoe is S1 or above, it has been through this test.
| Class | Energy absorbing heel | What else the class brings |
|---|---|---|
| SB | No, unless separately marked E | The 200J toe cap and basic requirements only |
| S1 | Yes | Closed heel region and antistatic performance |
| S1P | Yes | S1 plus a perforation-resistant midsole |
| S2 | Yes | S1 plus water resistance of the upper |
| S3 | Yes | S2 plus perforation resistance and a cleated outsole |
| S6 and S7 | Yes | The newer waterproof constructions |
SB is the exception again, which is why it keeps catching people out. A basic SB shoe covers the toe and little else, as we set out in what SB means and what it does not cover. Everything from S1 upward includes the energy absorbing heel by definition, so a product page that advertises it as a special feature is telling you something the class code already guaranteed.
Inside the Test, Step by Step
The method is more brutal and more specific than the phrase "shock absorbing" suggests.
- A shaped punch goes inside the shoe. Testing uses a set of backpart punches made from standardised lasts, and the one matching the shoe's size is selected so the load is spread the way a real heel would spread it.
- It is brought down onto the centre of the heel. The punch contacts the inside of the shoe at the middle of the heel area, so the whole sole structure beneath it takes the load.
- The load is applied slowly. Compression runs at a rate of 10 mm per minute, which is a deliberate, controlled squeeze rather than an impact.
- It continues until 5,000 newtons. That is the end point, and the sole is compressed all the way there.
- The energy is the area under the curve. Absorbed energy is calculated by integrating the load deflection curve between 50 N and 5,000 N, reported to the nearest joule, and it must not be less than 20 J.
Energy is force multiplied by the distance the sole compresses. A thick soft sole that squashes a long way can absorb the same energy as a firmer sole that compresses less but resists harder. That is why two shoes that feel completely different underfoot can produce similar numbers, and why the figure alone cannot tell you which one you will prefer.
Why 5,000 Newtons Is Not a Footstep
This is the part worth sitting with, because it reframes the whole marking.
Gait research puts the peak vertical ground reaction force in normal walking at around 107 per cent of body weight during the loading phase just after heel contact, with the force through a stride typically moving between roughly 80 and 120 per cent of body weight. For an 85 kg worker, body weight is about 834 newtons, so the peak is somewhere near 890 newtons.
The test compresses the heel to 5,000 newtons. That is roughly five to six times the peak force of a normal walking step, applied once, slowly, to a brand new shoe.
The test and the workday are different events
Both matter, but only one of them is certified.
The laboratory test
A severe single squeeze
Your actual shift
Mild loads, endless repetition
So the test proves the heel structure has real capacity. It answers the question "can this sole soak up a heavy load without bottoming out", and that is genuinely worth knowing. What it does not do, and was never designed to do, is model a ten hour shift. Fatigue is a story about thousands of small repeated loads, and this is a single large one.
What the E Marking Does Not Tell You
Four limits are worth being clear about, because most of the disappointment around cushioning comes from expecting the letter to cover them.
- It is a threshold, not a score. 20 J is a floor. A shoe scraping past it and a shoe comfortably beyond it both print the same E. The marking cannot rank two products.
- It is measured on a new shoe. Certification captures a moment. Nothing in that letter describes what the heel is doing after six months of daily compression.
- It says nothing about the forefoot. The test is the seat region only. If you stand still for long periods, a good deal of your loading is through the ball of the foot, which is not part of this assessment at all.
- It is not a comfort claim. Comfort depends on fit, volume, insole, upper, weight and how your particular foot loads. Energy absorption is one input among many, and the standard makes no promise about how anything will feel.
Treat E as a floor that has been cleared, not as a feature that has been won. It tells you the heel is not hollow and not brittle. It cannot tell you whether this shoe suits your feet, and no marking can.
Where the Cushioning Actually Comes From
The letter is certified, but the feel comes from the midsole material sitting between your heel and the ground. That is the part worth reading on a spec sheet.
| Material | How it behaves underfoot | The trade-off |
|---|---|---|
| Polyurethane (PU) | Resilient and supportive, holds its structure well over a long day | Denser than EVA, and susceptible to breakdown with age and moisture |
| EVA | Very light and soft on first wear, which is why it feels immediately comfortable | Compresses permanently over time, so the cushioning fades |
| PU and EVA combined | EVA for lightness with a PU or rubber layer for durability and grip | More complex construction, and the two layers age at different rates |
| TPU inserts | Used in the heel for structure and energy return rather than softness | Adds firmness, which not everyone wants under the heel |
If you are weighing up the two you will meet most often, PU and EVA outsoles compared goes through the differences properly, and what workers should know about EVA covers the softness-versus-longevity question on its own.
How Heel Cushioning Fades
The certificate does not expire. The cushioning does. This is the single most useful thing to understand about the E marking, and nothing on the box mentions it.
- Compression set. Foams do not fully rebound after being squashed thousands of times. The cells collapse gradually and the midsole thins, which is why an old sole can look intact and feel dead.
- Material breakdown. Polyurethane degrades over time in the presence of moisture, a slow chemical process that continues whether the shoe is worn or sitting in a cupboard.
- Uneven loading. Most people wear one edge of the heel faster, so cushioning becomes asymmetric long before the sole looks worn out.
None of this is a defect. It is what foam does. The practical consequence is that heel comfort should be judged by how the shoe feels now rather than by a letter printed when it was new, and a pair that has gone flat is worth replacing even if the toe cap and upper are fine. The wider cost of getting this wrong is something we looked at in the hidden cost of heavy safety shoes, and the physical side in what happens to your feet after ten hours.
The Insole Is Part of What Gets Tested
One detail follows directly from the method. The punch presses against the inside of the shoe, which means everything sitting in the heel at that moment forms part of what is being compressed, including the removable insole the shoe was supplied with.
That has a practical consequence people rarely think about. Throw away the original insole and drop in a thin flat replacement, and the heel you are standing on is no longer quite the one that was certified. It may well still be fine, and for many people a better-fitting insole is a clear improvement, but it is worth knowing that the tested configuration is the shoe as it came out of the box rather than the shoe as you have modified it.
Five Questions Worth Asking
- Is the shoe S1 or above? If so, the energy absorbing heel is already included and does not need to be sold to you as a bonus.
- Do you walk or do you stand? Walkers load the heel repeatedly. Standers load the forefoot, which this test never touches, so heel cushioning is less of the story for them.
- What is the midsole made of? The material tells you more about how the shoe will age than the certification does.
- How old is your current pair? If the heel feels flat, it probably is, regardless of what the shoe passed when new.
- Does it actually fit? A heel that slips wastes cushioning, because the foot is moving relative to the sole rather than loading it cleanly.
The Honest Verdict
The E marking is a real, measurable property with a precise test behind it, and it deserves neither the shrug it usually gets nor the weight marketing puts on it. It certifies that a new heel absorbed at least 20 joules under a slow compression to 5,000 newtons. That proves capacity. It does not promise comfort, it cannot rank two shoes against each other, and it says nothing about month six.
The useful takeaway is narrow but genuinely practical. Stop shopping for the letter, because every S1 shoe has it. Shop instead for the midsole material, the fit, and how old your current pair is, because those are the three things that actually change how the end of a shift feels.
On ours: the Xnexz PulseX and StrideX are certified EN ISO 20345 S1P, so the shock-absorbing heel is part of that certification, exactly as it is on every other S1P shoe on the market. We are not going to claim that makes your feet feel different at hour ten, because the standard does not measure that and we would be guessing. What we would rather do is hear from you after a real week in them. Full detail on the code is in what S1P certification actually covers.
If S1P Is Accepted Where You Work
Try Xnexz in a real workday and tell us honestly how the cushioning, fit and comfort hold up over a full week, and what we should improve. If your site needs a higher rating or specialist protection, buy what your safety officer specifies. That comes first.
Frequently Asked Questions
What does E mean on safety shoes?
E means energy absorption of the seat region, which is the heel. To carry it, the heel must absorb at least 20 joules when compressed in a laboratory test. It is a minimum threshold rather than a comfort score.
Do all S1P safety shoes have an energy absorbing heel?
Yes. Energy absorption is part of the S1 base requirement, so it carries through S1P, S2, S3 and the newer S6 and S7 classes. SB is the exception, since a basic SB shoe only covers the toe cap and basic requirements unless separately marked E.
How is the energy absorbing heel tested?
A shaped backpart punch sized to the footwear is pressed into the inside of the heel and the sole is compressed at 10 mm per minute until the force reaches 5,000 newtons. Absorbed energy is calculated by integrating the load deflection curve between 50 N and 5,000 N and must be at least 20 joules.
Is 20 joules a lot?
It is a floor, not a target. Some soles clear it narrowly and others exceed it comfortably, and both print the same E marking. Because the standard reports only pass or fail, the letter cannot be used to compare two shoes against each other.
Does an energy absorbing heel reduce fatigue?
The standard makes no claim about fatigue, and neither should a seller. The test is a single slow compression on a new shoe, whereas fatigue comes from thousands of repeated loads over a shift. Cushioning is one factor among fit, weight, insole and the surface you work on.
Does the cushioning wear out?
Yes. Midsole foams take a permanent compression set over time, polyurethane degrades slowly in the presence of moisture, and most people wear one edge of the heel faster than the other. The certification describes a new shoe and does not expire, but the cushioning genuinely fades.
Does the E marking cover the forefoot?
No. The test applies to the seat region, meaning the heel, only. If your work involves long periods standing still, much of your loading goes through the ball of the foot, which this marking does not assess.
