A watch strap can be made from an almost infinite number of materials where the solution is only limited by the designers’ imagination and the manufacturer’s skill. However, the most common materials are leather, metals, synthetics, textiles and as always - combinations thereof. We will not cover adornments using inlays or precious and semi-precious stones as these are beyond the scope of this introductory text.
Leathers
All leathers are skins of animals or rawhide, specially prepared by a process called “tanning” to stabilize them and in so doing to prevent decomposition of the natural cells. As it is a natural material aging should be expected. This takes the form of subtle changes in color or suppleness. In addition, no two pieces of leather are identical even though similar. Leathers have specific properties unique to the species from which it was derived. The most notable ones are surface structure, toughness and softness. Colors however are usually a choice by the tanning company as requested by its customers and have often little resemblance to the natural animal skin before dying. In addition, for some applications where high stresses are expected, typically in car upholstery and furniture, multiple protective layers are added to the surface for durability at the expense of a slightly less natural look and feel.
Calf |
Calf Leather is made from young cattle, typically less than six months of age. It has the advantage of being softer than hide from older cattle and often shows fewer surface defects. It is the choice leather for many applications owing to its characteristics and wide availability in numerous colors, surface textures and styles. |
Buffalo
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A leather of similar strength to calf leather but with some distinct differences: its grain pattern or the distinct pebble-like texture that lends the final products often a more natural or vintage air. In addition, the leather is more forgiving to surface damage while it is also more breathable, making it suitable for a use in wider temperature ranges such as in fashion and furniture items It is among the most used leathers owing to availability and its natural look and suppleness. |
Alligator
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The skin of a reptilian both of the same order in the animal kingdom as crocodiles. However, as they are listed as endangered species by CITES (Convention on International Trade in Endangered Species), permits and extra documentation must be obtained and maintained throughout the supply chain for reasons of traceability. Only a small portion of the skin is suitable for watch straps such that a pleasing look of the final product can be achieved. Therefore and together with the added documentation, cost is considerably higher than for almost any other skin. |
Ostrich |
A uniquely textured skin that shows “bumps” where the live animal had its feathers attached. Ostrich is often used to render a sportier look on a strap. |
Lizard |
Similarly to alligator and crocodile skin but often with a smoother feel and much smaller, clearly delineated scales often in Diamond shape. |
Snake |
Like the legged reptilians the skin consists of scales that have a looser attachment notably towards its end. Very often the coloring is less uniform and quite often also patterned. Snake leather is considered an exotic skin. |
Shark |
A sturdy skin that feels smooth in one direction and like sandpaper in the opposite direction owing to the particular shape of the microscopic scales, called dermal denticles. They give the animal a hydrodynamic advantage of lowering drag, adding thrust and reduce the growth of parasites on its skin. Owing to the shark fin trade and the associated stigma the use of this skin is not widespread. |
Eel |
Very thin and supple yet strong skin that is very smooth. It usually comes from hagfish that is in biological terms not an eel despite looking like an eel. Owing to the shape of the fish, the leather comes in long and narrow strips with minor unique scarring along its length; pieces are often edge-sewn together where wider pieces are required. |
Horse |
A leather that is typically used for shoes but has seen growing use for watch straps owing to its strength and rarity. The leather is considerably more expensive than calf as only select parts of the horse hide can be used. Further adding cost is the lengthy tanning process involved that can take several months to turn the raw hide into the finished leather. |
Metal
Steel
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The choice material for buckles of watch straps, spring bars and ultimately complete bracelets made from stainless steel – an alloy exhibiting high corrosion or rust resistance, particularly when exposed to salty environments like sweat or seawater. It is available nowadays in good quality and in many different compositions. The preferred stainless steel is a medical grade steel having a low Nickel content for good bio-compatibility at the expense of more costly processing due to the materials' toughness. Density is around 7.8 g/cm3. |
Titanium
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The choice material for demanding applications owing to its inertness. Titanium forms a surface oxide film that protects it against corrosion. Excellent bio-compatibility at about two thirds the weight of stainless steel and often superior strength. These desirable qualities come at the price of a considerably more difficult machining process owing to Titanium's spring back during cutting; this can lead to excessive tool wear in a very short time and so increasing cost. Most widely used Titanium is alloyed for better characteristics in machining and polishing. Density is approximately 4.5 g/cm3. |
Precious Metals
Gold
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The choice precious metal cherished over centuries by humans for its natural luster. However pure gold is too soft and in modern watch applications typically an alloy of 18 karat and in rare cases 14 karat is used. 18 karat means 750/1000 parts alloy between gold and one or several alloying metals. Depending on the alloying metals and the amount of them added either pink, rose, red gold or white gold results. The former is achieved by adding increasing amounts of copper while the latter is often an alloy with Palladium or other “white” metals. Density of pure gold is 18.9 g/cm3 or for 18 karat yellow gold around 16.4 g/cm3. |
Platinum |
Rarer and heavier than gold and in a lustrous white color; the typical alloy consists of 950/1000 of platinum. It is also the heaviest of the precious metals in use in the watch/jewelry industry. While in the past the price was almost twice that of gold while after the 2008 financial crisis it dropped to around the same as for gold. The main price driver in the past, apart from speculation was the automotive industry in their use of Platinum in catalytic converters. However, Platinum has been successfully replaced with lower cost alternatives and/or design improvements. Yet, a premium must be expected due to the difficulty in machining platinum as it behaves quite “gooey” and tends to wear out tools much faster than gold. Density is typically around 21 g/cm3. |
Silver |
Silver is less used in watches than during the time of the pocket watch. The most wide spread form is 925/1000 alloy often referred to as Sterling Silver. Nowadays predominate use is in jewelry and in the process industry and the occasional dial face. Density is typically around 10.5 g/cm3. |
Palladium
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It is a silvery-white metal of the platinum group of metals (PGM) that is also the lightest of them. Being comparatively soft it has only recently found application in the watch industry, while most of it is used as a substitute in catalytic converters for the considerably more expensive Platinum. Density is typically around 12 g/cm3. |
Other Metals
Tantalum |
Similarly to Titanium and Aluminum it forms a protective oxide layer on its surface. However, unlike the other two metals it is two to four times as heavy, having a density similar to gold. It has a dark grey-bluish appearance and is an attractive complement together with some of the noble metals. Machining is difficult like Titanium due to its “spongyness” leading to rapid tool wear. Density is typically around 16.7 g/cm3. |
Bronze
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Bronzes are alloys predominantly made of copper and tin often with the addition of select other metals. Depending on composition the color of bronzes range widely from a soft yellow over brown/red to almost white. Bronze is a preferred and cost-effective metal for marine use. Recently, a number of watches have been introduced using select bronzes, giving a design a more rugged look and feel. Typically, bronzes also form a surface layer that prevents further corrosion like Aluminum, Titanium and Tantalum yet at considerably lower cost and ease of machining. Density is typically around 8.9 g/cm3. |
Aluminium
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A soft ductile white metal that is comparatively easy to machine. It finds application in a few watches, decorative elements like bezels that are often anodized (colored) and in low cost pin clasps. While easy to machine its softness is the main drawback as it tends to wear out quickly in these applications (unlike in aircraft design, where stresses are dealt with through engineered solutions). Density is typically around 2.7 g/cm3. |
Synthetics
They form the widest selection of materials we can imagine, having been fine-tuned over the years to achieve ever better characteristics. These are often chosen for specific applications too numerous to list here. Naturally almost any color or combination of colors can be achieved and taken together with texture and technical characteristics afford the designer enormous freedom for a particular application.
One big advantage of synthetics is that they can be molded into almost any shape the designer of a product envisions, from thinnest threads to most complex shapes. The most widely used synthetics in watch straps are:
Nylon
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Developed by DuPont in 1935. In watch straps it is most often used as a fabric and depending on the variety has very good abrasion resistance making the watch strap very durable and comparatively cheap. Ballistic nylon is a denser form of nylon, originally used for military applications for extra protection against shrapnel. It is often used for pull-through or so called NATO straps. |
Polyurethane (PU)
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Developed by IG Farben (Germany) in 1937. Again numerous variations exist today from many suppliers. PU fabrics are available often as a blend with other synthetics. The best known PU fabric blends are Ultrasuede™ and Alcantara™. However, PU watch straps are typically molded and more recently saw it as a base in combination with other materials such as leather. Sometimes PU straps are also referred to as “Resin” straps. |
Silicone Rubber (SR) |
SR consists of polymers with silicone. “Rubber” in this context is a bit of a misnomer and is colloquially used owing to Silicone’s flexibility and feel but not its chemical characteristics in comparison to natural rubber. Unlike natural rubber where some people exhibit sensitivity to, SR is typically hypoallergenic and wears very nicely on the skin, having a very supple feel. It is a material that is very stable even under significantly elevated temperatures unlike PU or nylon. Again watch straps made from SR are typically molded and/or combined with other materials such as leather. |
Natural Rubber |
Derived from the rubber tree sap called Latex and vulcanized into the final product. These watch straps are almost exclusively molded. It should be observed that some people are sensitive to natural rubber. A good alternative in these cases could be a Polyurethane or Silicone strap. |
