Linings for footwear, these unknown components
“What is essential is invisible to the eye,” said the little prince. you will forgive such a profound quote, but it seems to have been purposely written to introduce an article dedicated to shoe linings, an essential element of which little is spoken, and perhaps little is known, but which plays a fundamental role in determining the quality of a shoe.
This article was written with several objectives:
• Together with colleagues from Arsutoria School, we have tried to explain the technical characteristics and functions of the lining inside a shoe;
• With ICEC, we have explored the world of chemical and physical tests;
• Together with some companies specialised in the production and marketing of linings, we have tried to understand how the market demands are evolving;
• Finally, we have interviewed spokepeople at two major companies of the sector and studied their point of view on the topic, in particular on the challenges that a shoe factory faces today when it comes to shoe linings.
This article is dedicated to shoe manufacturers who, day after day, are confronted with the use of many different materials. We hope, however, that it will also be read by designers who are already working in the footwear industry or want to work in it, by those who work in the retail world and are curious to understand how a lining can make the difference in a quality shoe and, why not, also by end consumers who are curious to know more about the shoes they buy and use, even from a more technical perspective.
The lining of a shoe is the part in contact with the foot
The first and most important function of the lining is to stay in contact with the foot. The foot remains enclosed inside the shoe for hours, sometimes not moving, sometimes moving. The foot may sweat and perspiration is one of the main mechanisms by which the human body regulates the temperature. From these first simple considerations, you can already understand that:
• The material that comprises the lining must guarantee the health of the wearer: the skin must not come into contact with any harmful substance;
• The lining must not fade, but above all, there must be no transfer of colour from the lining to the foot or the sock;
• The softness of the lining gives a feeling of comfort to the foot;
• Any creases or seams in critical points can cause blisters on the foot;
• The breathability of the lining is fundamental.
Do all shoes have a lining?
Actually no. There are so-called “unlined” shoes in which the foot is in contact with the inside of the upper, the so-called ‘flesh’ side, if the upper is made of leather. Unlined shoes are worn especially during the summer season, when the shoes are deliberately deconstructed and very soft (for example, moccasins). In theory, all models of shoes can be made without a lining or with a half-lining. When there is no lining in the construction of a shoe, it will clearly be necessary to pay more attention to some elements of the upper:
• Choose suitable materials that retain their shape (e.g. thicker leather),
• Evaluate the seams in direct contact with the foot,
• Carefully work the inside of the upper material (e.g. remove any residual hair from the flesh side of the leather)
Aesthetics and recognisability
At the beginning of this article, we said that the lining is invisible. This is true when we wear the shoe, however, the lining becomes clearly visible when the shoe is displayed in a shop window.
Evidently the more ‘open’ the shoe, the more visible the lining: the lining of a sandal is almost entirely visible, while in a laced shoe – which is usually displayed in the shop window with the toe and the outer side in the foreground – the most visible parts of the lining will be the part on the inside and the one in contact with the heel. Designers are very attentive to the aesthetics of the lining, and one of the most important elements of the shoe is found right on the lining: the brand logo. A variety of colours are used for the lining: ivory and biscuit-coloured as well as black are the most common, but fashion today requires many different shades and the possibility to offer a wide range of colours in a short time is becoming a critical success factor.
The lining and the foot that goes in and out of the shoe
You must have all worn a boot or an ankle boot at some point. So you know how complicated it is to slide your foot inside, and just how difficult it is to get it out, especially if the boot leg does not have a zipper. Here, then, is another important function of the lining: it must make it easy to slide your foot in and out of the shoe. For this reason the lining is usually smooth: you may have noticed that suede is not used for the lining. The only part of the lining where a material that creates a little friction is used the so-called heel pocket i.e. the part of the lining that wraps around the heel and that has the function of preventing the foot from coming out of the shoe while walking.
The lining helps give to structure to the upper
Walking and use in general tend to deform the shoe which, over time, loses its original shape. The material used for the lining and the way it is constructed help to determine how much the lining itself contributes to maintaining the shoe’s original shape. The amount of glue applied between the upper and lining also plays an important role: an excessive layer of glue may promote the formation of creases that appear mainly in the front part of the upper, where the foot bends. Years ago, it was usual to distinguish the materials used for the different parts of the lining: a softer cowhide was used in the front part of the lining for greater comfort and stiffer goatskin was used on the sides to counteract the natural widening of the area where the foot enters and exits the shoe.
What is a lining made of?
Different types of materials are used for the lining: leather, fabrics, technical or synthetic materials. In higher priced elegant shoes, leather is traditionally used. Goat or sheepskin leather is generally synonymous with a quality lining. It is usually used in fine women’s footwear, but sometimes we also find these linings inside men’s shoes. Calfskin, which is softer and has a slightly less robust structure, is frequently used in men’s shoes and sneakers made in Italy. The leather used to construct the uppers of classic men’s footwear is thicker than the leather used for women’s footwear and therefore the lining does not have to contribute much to maintain the structure of the shoe. There is calf leather, the so-called ‘vacuum’ which after tanning is dried with a system that gives the fibres a particular structure, while preserving their softness. Lower-priced shoes also use leather from other less prized animals, such as pig skin. This material, which is off-limits in shoes destined for Arab countries, has the unquestionable advantage of costing less, as well as being a leather with pores large enough to ensure greater breathability.
Lining and breathability
In order for a shoe to be breathable, it must guarantee the possibility of dispersing sweat towards the outside. Therefore, all those processes that cover the grain of the leather and obstruct and hinder the passage of air and water (sweat) towards the outside should be avoided as much as possible. A heavy finishing layer sprayed on the leather or a foil applied on top of the grain are all factors that limit the breathability of the shoe, as well as an excessive layer of glue applied between the lining and upper.
Design and production of the lining
One of the construction details of high-end Italian shoes is the way in which the lining is worked during assembly: in quality shoes, the lining is first pulled over the last and then the upper is assembled. This process takes longer, but guarantees fewer creases and imperfections. The linings are usually basted with a very light layer of glue and joined to the upper by sewing the edges. As already mentioned, it is essential not to apply too much glue between the lining and the upper. Although it may seem to help the workmanship by blocking the two materials together with glue, in actual fact it causes wrinkles that not even ironing can eliminate.
Tests and certifications
The hottest and most current topic in the lining world is probably that of tests and certifications, which are increasingly requested by customers, especially major brands. Challenging activities both in terms of the time needed to carry out the tests and in terms of costs. We discussed this with the ICEC, the Italian Certification Institute specialised in the leather area, created in 1994, and promoted by the Italian Association of Tanneries (UNIC), whose members also include several stakeholders in the leather industry, such as the associations of footwear and leather goods manufacturers.
What are the certifications that concern leather for linings?
“There are two levels of certification: system certifications, which cover the entire company (environmental, social, quality, etc.) and product certifications. The latter focuses on different aspects:
• the traceability certification, which describes the origins of the raw material;
• Made In Italy certification, which verifies where the main stages of the tanning production process were carried out;
• the certification according to the UNI 10594 standards for leather to be used in the footwear industry is a voluntary certification specifically for companies, which carries out laboratory tests, both chemical and physical, to investigate the characteristics of leather intended for the production of shoes and, therefore, also linings.”
Does the UNI 10594 specification have specific requirements for lining leather?
“The specifications of the standard refer to leather in general, i.e. no different limits are set for the specific use of leather as a lining. Although, in fact, since lining leather comes in direct contact with the skin of the wearer of the shoe, it would make sense to pay attention to this specific aspect. This is a different matter if we go into the subject of a company’s specifications where, for the same test, more stringent and precautionary limits can be set depending on the type of use of the leather.”
What developments are planned for the new version of this ISO standard?
“The new UNI10594:2019 version has reduced the substances to be monitored to formaldehyde (and the limit of contact with the foot has been reduced to 75 ppm) and to penta and tetra chlorophenyl. Tests for chromium VI and azo dyes are no longer foreseen. The physical tests required by the standard are: abrasion resistance (dry and wet), permeability to water vapour, fastness of dry colour, colour deterioration with artificial sweat, discharge of colour to rubbing with artificial sweat, colour fastness to perspiration”.
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