The testing of shoe care products
How shoe care products can be tested to ensure that they perform well and meet customers’ expectations.
by Mark Southam
Whatever their purpose, it is important that shoe care products work well. Although a customer’s expectation of such items may sometimes be unrealistically high, any claims that are made on the packaging or advertising should still be met. It is also important that applying the product does not have any adverse effects on the upper (or, indeed, any other part of the shoe) which might, for instance, make it look unsightly or cause degradation over time.
There are a number of tests for effectiveness that can be carried out, depending on the particular product type. Assessing how a polish, wax or cream improves the overall finish of an upper is usually best done subjectively – by applying the product to the type of material for which it is intended and assessing the change in appearance (for example, the level of gloss or any alteration in colour). It is also possible to measure gloss quantitatively using a ‘gloss meter’. This can be useful when comparing the performance of different polishes.
Measuring how well a product can repair damaged uppers is also important. This can be done by subjecting a specimen of the upper material to scuffing abrasion using SATRA TM95:1996 – ‘Abrasion and snagging resistance – drum method’. The specimen can then be treated with a product that is appropriate to the specific upper material, after which a subjective assessment is made on how well the damage has been repaired. The effectiveness of the product on different levels of damage (such as deep snags or mild scuffs) can be assessed.
Waxes and creams are often applied to leathers to improve or give a degree of water repellency. A simple method to check their effectiveness is to assess how much water can be absorbed into the surface of the leather. SATRA TM198:1999 – ‘Evaluation of surface water repellency – shoe care products’ can be used to determine this. In this test method, the surface of the specimen is exposed to liquid water for a short period of time, and the amount of absorption is assessed by weighing the test piece before and after exposure. However, repellency is usually only temporary, as flexing and general ‘wear and tear’ will soon open up the film, allowing water to penetrate. The test is, therefore, carried out after the material has been flexed (using the method in SATRA TM25:1992 (2016) – ‘Vamp flex test – resistance to creasing and cracking’), to measure the treatment’s overall effectiveness. The test needs to be carried out on both the treated and untreated materials in order to see how much the product can improve repellency.
For products which actually claim to make footwear materials ‘waterproof’, a more severe test should be used. SATRA TM34:1993 (2009) – ‘Resistance to water penetration – Maeser test’ flexes a piece of the treated material, outer face down, in a trough of water. The number of flexes before penetration through to the reverse side occurs (if at all) is measured. However, although some products may help to improve short-term water resistance, it is highly unlikely that they could make footwear genuinely ‘waterproof’ for extended periods of wear.
Some products are designed to repel water and oils in order to reduce the severity of staining from contaminants spilled or splashed on the footwear. Their effectiveness can be assessed using SATRA TM201:1999 – ‘Water and oil repellency – shoe care products’, which uses a series of eight mixtures of isopropyl alcohol and distilled water in different proportions. Each mixture has a different level of ‘wettability’, and these are applied in turn to the treated material. If the spot is not absorbed within ten seconds, the next liquid in the series is applied to another area of the treated material. The higher in the series the specimen reaches without absorption, the better is its performance. Oil repellency is assessed in exactly the same way, but using eight different oil types of varying viscosities.
Improving water repellency can also reduce the risk of drops of water (for example, rainwater) from causing watermarks or blisters on the surface of the upper. This is generally an issue with grain leathers, nubucks and suedes rather than coated synthetic materials. Watermarks (or ‘tidemarks’) are caused by movement of loose dyes in the leather. Blisters can be caused by the water being absorbed and swelling the leather fibres. A simple water spotting test – SATRA TM185:1995 – ‘Colour fastness to water spotting of leathers, textiles and coated fabrics’ – can identify which upper materials are susceptible to such damage and, more importantly, which shoe care products will be best to protect the materials in question. In the test, two drops of water are placed on the upper; one being left for 30 minutes and the other for 16 hours, to see if watermarks or blisters occur. The test can then be repeated with the shoe care product applied to the material.
Protection against staining
How efficiently shoe care products protect against marking by muddy water can be measured using SATRA TM200:1999 – ‘Resistance to mud staining – shoe care products’. A specimen of standard compost is shaken with water, after which the mixture is spotted onto the treated upper material as well as on an untreated piece, which acts as a control. After drying, the deposit is brushed or wiped off the material, and any residual staining is noted. If the product is also designed to clean footwear as well as protect it, a further application can be applied to assess the cleaning efficiency.
If a product forms a distinct layer or coating on the upper, flexing tests are useful to determine if this coating is likely to crack, flake or peel when the footwear is in use. Even very fine cracking or crazing can cause unacceptable whitening of the upper. SATRA TM25 (figure 1) is ideal for assessing this risk. The product is applied to a specimen of upper material and, after drying, it is flexed to see if there is any change in appearance. The product is then reapplied and flexing continues – a process that is repeated several times. Flexing after multiple applications is important. This is because the initial layer may be satisfactory, but several applications may produce a build-up of product which is more prone to cracking or flaking than just a single layer.
Coverage of dyes
Recolourants and dyes may be assessed subjectively for coverage by applying them to contrasting colours, such as whites applied to black and vice versa. This is a valuable guide to their effectiveness in use. After drying, physical testing – for instance, assessment of flex and rub fastness – will ensure that it is sufficiently stable on the upper material to prevent loss during wear.
Heavy applications of products could also affect the breathability of the footwear by sealing the surface of the upper and preventing water vapour escaping. This will have a direct effect on the wearer’s comfort and is certainly important where the footwear is designed specifically to offer good moisture management properties. Outer materials can be assessed for breathability before and after application of the product to see if any change in performance is likely to be significant. SATRA TM47:2002 – ‘Water vapour permeability and absorption’ is the most appropriate method for doing this. As flexing of the material may help to break up the finish which could improve its breathability, additional breathability tests after flexing may also be helpful. Re-testing after multiple applications may also be beneficial to see if a build-up of several layers has a cumulative effect on breathability.
Shoe care products can play a significant role in after care of footwear, both for appearance and durability. Members can have their products assessed by SATRA to confirm their effectiveness.
How can we help?
Please contact SATRA’s footwear testing team (email@example.com) for assistance with the testing of shoe care products.
This article was originally published on page 46 of the May 2018 issue of SATRA Bulletin.