The value of digital last assessment

Digital last assessment can help in catching mislabelled sizing and poor fit characteristics at an early stage, expediate design and production and decrease development costs.

by Zach Armitage

Digital last assessment is a process in which the likely fit characteristics of footwear made on a last can be predicted. The volume created for the wearer’s foot within any item of footwear is predominantly determined by the shape and size of the last on which it is manufactured. Other variables also play a role in the final fit of the product, including the construction method of the footwear, the upper and soling materials and the style of footwear and fastening systems. Predominantly, however, it is the last that forms the characteristics of the final shoe.

E-commerce has more than doubled between 2012 and 2018 and in the USA alone it is worth an estimated $517 billion (£395.9 billion). Some reports indicate that 30 per cent of online sales are returned, with footwear making up 17 per cent of all online returns in Germany during 2019. A large proportion of all footwear returns are due to poor fit. The problem of poor fit, mislabelled sizing and confusion for the end consumer on the suitability of a product can be reduced with a better understanding of the last, its dimensions and its effect on the shape and fit of the final item of footwear.

SATRA offers three digital last assessment services in order to help to determine fit characteristics and appropriate size marking during the digital design stage. Fixing possible problems during digital design will prove to be vastly cheaper than finding mistakes later in the design and manufacturing process. A three-dimensional (3D) file of the last can be sent to SATRA and precise measurements taken, to be compared to either the well-established SATRA guidelines or, alternatively, to a retailer’s or manufacturer’s guidelines.

Last verification

Last verification uses precise digital measurement to confirm the last dimensions stated by the manufacturer. In this way, retailers and manufacturers can use the SATRA last verification service to have the dimensions independently verified. This offers greater confidence between retailers and manufacturers that footwear produced on their lasts will conform to the dimensions agreed by both parties.

Last assessment

This service is an assessment of the last dimensions in which the measurements of the last are reviewed by experts and compared to SATRA guidelines to determine if the last is suitable for purpose. SATRA last assessment will provide a statement of the fit characteristics of the last and conclusions on the marked size, including suggestions on improvements or recommendations for alternative size labelling.

Fit forecasting

SATRA’s fit forecasting service offers a comparison of the measured last dimensions to the large-scale foot dimensions study that SATRA has been conducting over the last five years. In this way, a prediction of population coverage is provided. If a last has been designed for a particular target audience, such as women aged 35 to 55, the dimensions of the last can be compared to this group and a population coverage value calculated. In addition to this prediction, suggested amendments to the last dimensions are made in order to maximise population coverage. This is useful when a generic last is being designed for a large target audience.

Once physical samples of the finished footwear are available, SATRA recommends that the definitive way of determining fit characteristics and size is to perform a SATRA TP4 fit assessment. This involves the final product being fitted to several human models and a trained expert assessing the fit on the foot. The model can be asked for his or her opinion on the fit and comfort, and this data is collated to make a statement of the size with which the footwear should be marked, and the fit characteristics offered by the product. This might be expressed as ‘men’s size UK 9, but with a generous joint girth and breadth more suited to wide feet’.

Each model on the fit panel has his or her foot measurements taken precisely before the assessment of the footwear, and the panel is deliberately made up of individuals with slight variations in foot morphology. In this way, an individual with a wide, long foot for the marked size will express that the footwear is slightly short and tight compared to an individual with a short, narrow foot for the marked size. A concise fit assessment with a good range of foot models will even be able to accurately express the internal dimensions offered by the footwear.

There has been growing interest in using cavity scanners to produce a 3D image of the internal space of footwear. While these can offer an indication of available space and a rough estimate of size, they cannot take into consideration the flexibility of materials, and will underestimate the available space. A soft upper trainer with a memory foam insock will appear to have much less available space than in reality, as the foot compresses the insock and the upper stretches and moves the materials to provide a larger volume. However, scanning the internal space of footwear may be useful as a quality control procedure to determine that similar products have a similar shape and volume.

While a SATRA TP4 fit assessment is incredibly useful, it is only available as a tool for finished footwear. If there are problems with the fit and the marked size, steps must be taken and money spent correcting these mistakes. Typically, a fit assessment will occur during the ‘approved sample’ stage of development, where sample footwear is made to test for production problems, as this is likely the first time a finished production sample is available for assessment. SATRA is often approached with requests for fit assessment after full production has begun and comments from customers have prompted an investigation into the fit of a product. When issues in fit and size marking are caught in the design and sampling stage, they are much cheaper to deal with than after full production has begun.

Publishing Data

This article was originally published on page 38 of the February 2020 issue of SATRA Bulletin.

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