Learning from footwear failures – part 2
Concluding a two-part article which provides an opportunity to benefit from the negative product experiences of a group of diverse 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 with 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 gives the opportunity to assess what could have been done to prevent such difficulties. Part one highlighted the first 12 case studies. Now our report continues...
Case study 13: safety shoes. “Separation of outsole from upper around the flexing point, and excessive scuffing on toes – but I still wear them. The shoes are now about three months old and I won’t bother trying to return them to the retailer. I would have second thoughts about buying the same brand again.”
SATRA comment: “Sole bond failure is common, but is actually tested for in type-approval testing of PPE footwear. Therefore, a prototype of this shoe – at the minimum – had been bonded satisfactorily, although of course that gives no guarantee about subsequent production. Producers and suppliers must definitely take note of ongoing quality control.”
Case study 14: walking boots. “After ten miles, I was suffering pain in the front of my foot rather than at the heel.”
SATRA comment: “Tests for underfoot cushioning (SATRA TM183:2018 – ‘Whole shoe cushion assessment test’) and shock absorption (SATRA TM142:1999 – ‘Falling mass shock absorption test’) are particularly appropriate for this type of product. The second method is capable of assessing the heel and forefoot areas separately. Another property is ‘ground insulation’, which is evaluated in SATRA TM190:2002 – ‘SATRA ground insulation index’. This also relates to underfoot discomfort, but is caused by soles being too thin or too flexible, and thus transmitting concentrated pressure. This test is very appropriate to the forefoot area, which tends to be thinner than the heel in hiking styles. Footwear producers often only ask for shock absorption testing on the heel rather than on both the heel and the forepart. However, research has shown almost identical pressures in both the forepart and the heel. Alternatively, these boots may just have been a poor fit and too close in the forepart. We would need to examine the worn footwear to confirm whether this was the problem.”
Case study 15: safety boots. “Two weeks after buying these boots, the upper started cracking, and this failure stopped me from wearing them. I was told by the supplier not to return them, as they would send me a new pair. These arrived and had the same problem. I doubt that I would buy from this company another time.”
SATRA comment: “Testing the upper in line with SATRA TM25:2020 – ‘Vamp flex test – resistance to flexing damage’ could be used to ascertain if flexing is satisfactory. As it is a safety boot, perhaps this is a coated leather that has been damaged by hydrolysis due to excessively long storage or storage in poor conditions, prior to sale. This could also be an issue with fit. If the boots are too generous in the forepart – that is, too deep – flexing will be very severe. The other issue is the length of the steel cap. The flexing will be concentrated in a small area behind the back edge of the toe cap. This will be even more exacerbated if the fit is deep as mentioned above.”
Case study 16: walking boots. “Seeing poor stitching in the lining in the toe region actually led me to not buy the product. If I had purchased it, I imagine that I would not have walked far before blistering my toes.”
SATRA comment: “An examination of the footwear would be necessary to understand what is meant by ‘poor stitching’, as the finish may have been within the accepted levels of ‘normal shoemaking’. However, a genuine fault that could cause a blister is a safety-related issue, so finding such a problem in the store would indicate failures in both manufacturing and quality control processes. Such a situation should be investigated to see if a style/batch is inherently faulty – and if it is, what corrective action is required.”
Case study 17: rubber-soled deck shoes. “The Sole cracked when it flexed, even after light to moderate wear. This problem stopped me wearing the shoes, so I return them. I would be cautious of buying the same brand again.”
SATRA comment: “Rubber soles normally have good flex crack resistance, but this case study perhaps highlights that this should never be taken for granted. We have seen an example of another deck shoe on which the sole compound had become very hard and brittle. For a shallow patterned sole such as a deck shoe, SATRA TM60:2020 – ‘Ross flex test – resistance to cut growth on flexing’ could have identified a sole flexing weakness during pre-production. Other basic physical tests such as strength and extensibility (both in SATRA TM137:1995 – ‘Tensile properties of plastics and rubbers’) might also have provided early clues to the rubber sole factory in deciding whether to choose a potential material – or choose a composition if making the rubber themselves – even if they don’t have any flex testing data.”
Case study 18: women’s boots. “The footwear failed at the seam, with tearing of the upper – apparently due to little stitching margin.”
SATRA comment: “If this is a case of poor seam allowance as the wearer suggests, the quality control process was at fault. However, it could also have been as a result of poor material quality or insufficient reinforcement. The edge of the leather component could have been over-skived, making it too thin and reducing its strength. It may even be that the wrong needle has been selected for the material being used.”
Case study 19: trainers. “Some aspects of the sole pattern broke, although the shoes were only three weeks old. The problem didn’t prevent me from wearing them, but as it demonstrated that these trainers would fail soon, I returned them to the retailer. I would buy from the same brand again, but not the same style.”
SATRA comment: “This failure may have been a result of flex cracking or tearing damage – for example, some of the tread cleats being ripped away. In the former case then a whole sole flexing test such as SATRA TM133:2017 – ‘Resistance to crack initiation and growth – belt flex method’ could have predicted the problem, whereas in the latter case the tear strength of the sole material may be assessed by such methods as SATRA TM218:1999 – ‘Tear strength of rubbers and plastics – trouser method’. Basic material quality characteristics – for instance, tear strength and abrasion resistance – should be assessed right at the beginning of the supply chain as part of the materials selection process, even before soles are produced.”
Case study 20: suede ankle boots. “My boots were left near a window for a couple of days and one of them faded to a totally different colour. I wouldn’t buy that brand again.”
SATRA comment: “Footwear materials should be assessed for light fastness by testing to SATRA TM160:1992 – ‘Colour fastness to light from a xenon arc’. Especially should all coloured leathers be tested for light fastness – particularly reds and blues. We have even seen black leather turn green, although this level of change is unusual.”
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Case study 21: fashion Chelsea boots. “The trim around the gusset and topline – a chain of small silver beads – came loose and started to hang down. The boots were less than a year old when this happened. I did send an e-mail to customer services and they told me to take them to a store to be assessed for a refund, but I never did because I don’t live near any of their stores. Unfortunately, there were issues with two different pairs I bought from this brand at the same time. However, because I still prefer the look and fit of their footwear, and I am aware that I can return the shoes, I expect that I would probably end up buying from them again.”
SATRA comment: “This may have been a result of poor-quality stitching or inadequate thread used to attach the beads. Either way, the factory seems to have had a poor quality control operation in place.”
Case study 22: children’s school shoes. “The outsole separated from the upper after six months’ wear. This obviously prevented my daughter from wearing the shoes, so I returned them to the retailer. I don’t think I would buy from that same brand again.”
SATRA comment: “This is yet another sole adhesion problem, which supports the previously-mentioned assertion that this is the most common type of shoe failure. Testing of production to SATRA TM411:2019 – ‘Peel strength of footwear sole bonds’ is vital to assure that good materials and processes have been used to achieve good results. Due diligence testing on bulk product is really essential.”
Case study 23: black slip-on shoes. “The problem was severe salt spue on the uppers of my new shoes when they became wet. This didn’t stop me from wearing them, as they were supremely comfortable and the spue could be removed each time. However, I would consider buying other brands instead in the future because of this experience.”
SATRA comment: “Chemical spot tests on the spue might indicate if it was chloride. This could indicate perspiration or road salt (hence not a justified complaint) or tanning salts, which could well be a good basis for complaining. It could also be worthwhile conducting a wet vamp flex test.”
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.
SATRA test methods now available online
SATRA test methods can now be purchased online. Please visit www.satra.com/test_methods to download the current catalogue and to order these documents.
How can we help?
Please contact SATRA’s footwear team (firstname.lastname@example.org) for assistance with testing at all stages of production.
This article was originally published on page 46 of the September 2021 issue of SATRA Bulletin.