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Learning from footwear failures – part 1

An opportunity to benefit from the negative product experiences reported by a diverse group of customers.

What type of footwear failures do consumers face today? A number of wearers were asked about their experiences, and these revealed some interesting problems – often with relatively new shoes and boots they had purchased or been given to wear by their employer – as well as how it made them feel about selecting the same brand again. The comments provide insight into the apparent failings of some materials and components, and provides an opportunity to assess what could have been done to prevent such difficulties.

Case study 1: safety shoes. “The problems I experienced involved sizing and durability. I ordered a new pair of the same type and size of shoe that I had previously bought – UK 12. However, the sizing came up small and the shoe was visibly smaller than my old pair, so I changed them for a size 13. The shoes were less than six months old when the lining started to disintegrate at the heel. This problem stopped me wearing the product and, although I didn’t return the footwear to the retailer, it would make me cautious of buying from this same brand another time.”

 

Footwear producers should consider testing the durability and quality of the linings used in their products

SATRA comment: “If the size 13 shoes gave a loose fit, this could have exacerbated abrasion due to heel slip. It is important to note, however, that the abrasion resistance of lining material can be assessed to see if it meets SATRA’s recommendations and the requirements of EN 20345. Linings on safety footwear must pass abrasion tests to be CE or UKCA marked. We wonder if the bulk product was representative of the samples submitted for type-approval. For due diligence testing and demonstrating ongoing conformity, footwear should be taken from the bulk delivery and retested periodically as stated in the technical file. Most companies only test safety critical properties on a regular basis, but this particular lining failure demonstrates that they should consider durability/quality testing as well. It is highly likely that the lining in this particular shoe was inferior to that initially tested.”

Case study 2: suedette Chelsea boots. “The boot seemed to ‘snap’ between the heel and the sole. Every time I put my foot down, the heel would alarmingly slide backwards. This was apparent from the first time I wore them. As the support had disappeared, I felt unstable, so I returned them and was fully refunded. They were from a catalogue’s ‘own brand’ low price range, and I would be definitely wary of buying the same brand again.”

SATRA comment: “It seems as though the heel came at least partly detached. This may reveal an inherent weakness in this style which should have been ‘due diligence’ tested for heel attachment strength prior to release. SATRA TM113:1996 – ‘Measurement of the strength of attachment of heels to footwear and the backpart rigidity of such footwear’ could have detected the problem and given the brand owner an opportunity to put it right before the product launch. Bulk production may be different to the sample initially tested. Sourcing companies and retailers should be selecting shoes from bulk delivery for due diligence testing – especially safety critical testing on fashion shoes.”

Case study 3: wellington boots. “The glue used to affix the brand label became visible as white smears across the top of the boot. The footwear was about two years old when I experienced the problem, and it did not stop me wearing the boots so I didn’t try to return them to the retailer. This would potentially make me consider whether or not to buy this footwear again, but I do love the brand – so I will probably continue to buy from this company.”

SATRA comment: “This is one of those cosmetic issues that just slightly spoils the enjoyment of otherwise good footwear. Ageing has caused the overspill adhesive to become more visible – this is largely a question of operator skill/training in the factory, and better shoe room examination and cleaning up of finished product. An accelerated ageing test of a boot sample would have been worthwhile, as would have given an evaluation of the adhesive for noticeable colouring or breakdown.”

Case study 4: trainers. “The sole of my trainers started to crack when they were two or three months old. I didn’t try to return them, but I would definitely be cautious about buying these particular shoes in the future.”

SATRA comment: “Sole flexing weakness can easily be detected by suitable testing during product development. Candidate sole units or the materials that have been selected for a particular style can be tested before the shoes are made. Methods include SATRA TM60:2020 – ‘Ross flex test – resistance to cut growth on flexing’, SATRA TM133:2017 – ‘Resistance to crack initiation and growth – belt flex method’ and SATRA TM161:2004 – ‘Bennewart flex test – resistance to cut growth on flexing’. This enables poor soles to be weeded out prior to production commencing. Sole unit samples can be also subjected to accelerated ageing and cold weather tested.”

Case study 5: hiking boots. “The midsole material deteriorated to the point where it fell out in chunks at the heel, and then the outsole split off. Although the boots were about ten years old, they had only been worn infrequently. I could no longer wear the footwear.”

SATRA comment: “This sounds like a classic case of hydrolysis breakdown of a polyurethane (PU) component caused by the passage of time and the attack of moisture contained in air of normal humidity. While this might seem like a fault with the footwear, it is possible that this material was as good as it could have been for its type, and the footwear has simply been kept for too long. However, it is difficult for the public to appreciate this unless warned by labelling on the product, which can advise on the best storage conditions (cool, dry and well ventilated). Predictive testing is available which involves monitoring of tensile strength after increasing periods of accelerated moist ageing. These results give rise to a predicted shelf life for the product. This includes the whole time after the sole was moulded – transit, warehousing, retail and service use by the wearer. Therefore, there really is a ‘use by’ date for such footwear.

“We have heard of many returns and complaints being made where consumers have purchased two pairs of a style, as they found the PU-moulded soles comfortable. When they get the second pair out to wear after the first shoes have worn out, the sole disintegrates when they start walking. SATRA TM344:1995 – ‘Hydrolysis of polyurethane solings and polyurethane-coated leathers’ can be used to verify fitness for purpose and to judge the effectiveness of formulations that are claimed to resist hydrolysis.”

 

Examples of hydrolysis breakdown of polyurethane (PU)

Case study 6: casual trainers. “The problem was hydrolysis of PU-coated leather. The shoes were around three years old when the problem started, and it did not stop me wearing them – nor would this difficulty make me cautious of buying the same brand again.”

SATRA comment: “This was likely to have been caused by the passage of time and the attack of moisture contained in air of normal humidity. It could also have been caused by poor storage. Three years is reasonable before footwear containing PU are affected by hydrolysis, especially if they have become wet.”

Case study 7: trainers. “From new, one of my trainers suffered from a clicking noise each time I walked. The problem didn’t stop me wearing them, but it was annoying. If I hadn’t bought them overseas, I may have returned them.”

SATRA comment: “This is an unfortunate problem. Noises from within a shoe are a nuisance without impeding the function of the shoe. At present, there is no standard test for it. However, when trying on shoes, prospective customers can listen out for such noises, as well as focusing on fit and comfort. Two components can sometimes audibly rub against each other in the shoe. For example, a noise like this can happen if the shank becomes detached from the insole and the two rub against each other when the shoe is flexed during walking. While it is conceivable that this could happen to every shoe within a given style, it is far more likely to be the odd rogue product, and would therefore be difficult to test for.”

Case study 8: fashion boots. “The sole detached from the left boot while I was wearing them. I had owned them for more than a year, but had only worn them perhaps seven or eight times. I could no longer wear them but, as I assumed it would be pointless to return them to the retailers so long after I bought them. I just threw them away. I won’t buy anything from that brand again.”

SATRA comment: “This appears to be a case of poor sole adhesion, which is probably the most common type of footwear failure. If the shoes were only lightly worn and still in otherwise good condition, it could have been worthwhile returning them because the fault would have been present from new. Footwear manufacturers test sole adhesion by methods such as SATRA TM411:2019 – ‘Peel strength of footwear sole bonds’ to verify whether the particular shoe evaluated is well adhered. However, it is still possible for some shoes within a style to be faulty for a variety of reasons (sole bonding is a multi-step process), even when good materials and processes are being used. The cause of the problem may have revealed itself upon expert examination. The supplier should have been performing due diligence checks.”

 

Poor sole adhesion is probably the most common type of footwear failure

Case study 9: walking boots. “Two of the eyelets broke, even though the boots were brand new. I had bought them online and could not be bothered to go to all the trouble of returning them, so I now wear them as everyday footwear around the house or when I drive. The problem I experienced would not stop me from buying the same brand again. I have bought a fair number of this style over the years because they are comfortable – and this is the first problem I’ve had. However, I am always cautious of buying some kinds of items online as you receive what they give you rather than you being able to physically choose what you buy.”

SATRA comment: “There are several reasons why the eyelet may have pulled out from the upper. If it was a two-part eyelet and the parts separated, the component may have not been clenched properly. Alternatively, the hole may have been too big or, if the upper surrounding the eyelet tore, the upper may have been too weak, with inadequate reinforcement having been used. Eyelet security can be assessed with SATRA TM150:1999 – ‘Attachment strength of eyelets’, and facing strength in accordance with SATRA TM149:1999 – ‘Strength of eyelet facings and other laced fastenings’.”

Case study 10: casual leather shoes. “The leather upper tore on my 18-month-old shoes and I could no longer wear them. I tried to return them to the retailer but my complaint was rejected. Would this difficulty make me cautious of buying the same brand again? Yes – I shan’t buy this shoe again.”

SATRA comment: “Examination of the tear might have indicated if the failure was as a result of poor leather quality – for example, loose fibrous structure and/or inadequate/lack of reinforcement (if the leather was good enough quality but too thin for use without reinforcement), which is the most likely cause. Testing of the leather for tear strength (SATRA TM162:2017 – ‘Tear strength – Baumann method’) might have been useful for the manufacturer, and this can sometimes be done on specimens from an area surrounding the tear. If the problem was as a result of inadequate reinforcement, this should have been picked up at the product development stage. However, there is no legal requirement to test fashion shoes other than the General Products Safety Directive (GPSD). This says that only goods that are safe to use can be placed on the market, but the failure described would not be regarded as safety critical. This failure could have been exacerbated if the footwear did not fit properly and there was undue strain on the uppers.”

 

Upper tearing is often a result of inadequate or even non-existent reinforcement

Case study 11: work boots. “The laces on my new work boots were so slippery that they would not keep tied together for longer than five minutes. I could no longer wear them and this has affected my view of this brand.”

SATRA comment: “Interestingly, the European standards for PPE footwear – which are quite comprehensive in most respects – do not consider the lace in any way. However, SATRA has a number of lace test methods for footwear in general, which include SATRA TM195:2004 – ‘Knot slippage test’. These tests can be carried out over and above the basic requirements of the PPE standards, as part of wider quality control. Knot slippage can become an important issue – a large company was fined a considerable amount when a child tripped over laces that slipped undone and the company had not tested for this problem. From a manufacturing point of view and in order to pass abrasion tests, the lace may need to be woven more densely and contain more fibres. This can create a smoother surface to the lace, with lower fiction, so it can come undone during wear. This is a common fault in safety footwear and uniform shoes, where durability is paramount. In situations where a high abrasion resistance is required, the knot slippage test should ideally be conducted.”

Case study 12: walking boots. “Although the footwear was specifically designed as walking boots, they were also worn as everyday wear/motorcycle boots. The problem Is that the sole inside the boots broke down in the heel area, making them uncomfortable to wear. I could no longer wear them. Up to the point that they wore out, I was happy with them. I figured that 12 to 18 months of constant wear from a £75 pair of boots represented reasonable value, as boots usually last me for a year.”

SATRA comment: “This sounds like microbiological breakdown of a cellulose insole board. Some wearers’ sweat can cause breakdown of the material and the insole material can break up and fall into the cavities in the sole. This can be very uncomfortable. If the failure had actually been premature, it may have been due to abrasion of the socking. Checking the abrasion resistance (in accordance with SATRA TM31:2003 (2014) – ‘Abrasion resistance – Martindale method’) may reveal if the lining is of a poor quality. If the breakdown was of the footbed foam, SATRA TM159:2018 – ‘Cushioning properties’ can assess its durability.”

Expert assistance is available

Understanding how your products perform in real-life situations is often key to manufacturing shoes and boots that are of a sufficiently high quality to encourage brand loyalty – a vital business concept in this highly competitive world. For more than 100 years, SATRA has been providing excellence in testing expertise to help organisations throughout the supply chain – from tanneries and component manufacturers to shoemakers and retailers – to help prevent prospective material and whole footwear failures. Part 2 of this article – considering other footwear failure case studies – will be published in a future issue of SATRA Bulletin.

How can we help?

Please contact SATRA’s footwear team (footwear@satra.com) for assistance with testing at all stages of production.

Publishing Data

This article was originally published on page 20 of the July/August 2021 issue of SATRA Bulletin.

Other articles from this issue »