bio-rubber

What is bio-rubber

Bio-rubber is a new generation synthetic elastomer obtained from the controlled polymerization of vegetable oils and biotechnological precursors, as an alternative to both traditional natural rubber and synthetic compounds derived from petroleum. Intensively developed in the early 2000s by European and Asian research laboratories, bio-rubber represents the evolution of polymer science towards renewable sources without compromising mechanical performance. Unlike natural rubber extracted from the Hevea brasiliensis tree, which requires extensive vulcanization processes and exhibits intrinsic variability in composition, bio-rubber allows for precise molecular control during synthesis, ensuring structural homogeneity and predictability in final properties. The raw material primarily comes from castor oil, soy, and other certified sustainable crops; the polymerization processes occur in controlled reactors at optimal temperatures and pressures, significantly reducing carbon emissions compared to conventional synthetic rubber. In the Italian watchmaking leather goods sector, bio-rubber has gained ground in the last eight years due to growing producer awareness of sustainability and the material's ability to offer elasticity, wear resistance, and dimensional stability superior to many traditional elastomers.

Characteristics and Properties

Bio-rubber possesses a multidimensional performance profile that makes it ideal for applications requiring durability and prolonged comfort. From a texture standpoint, the material exhibits a dense and uniform molecular structure, devoid of the micro-porosities that characterize vulcanized natural rubber. Softness is controllable through formulation: variants intended for watch straps are synthesized with vegetable plasticizers that ensure a soft and silky feel, without stickiness. Mechanical resistance exceeds 15 MPa (megapascals) in tension, maintaining an elongation at break of around 300-400%, providing controlled elasticity to the strap without permanent deformation. Chemical resistance is superior to natural rubber: bio-rubber effectively resists body oils, saline sweat, prolonged sun exposure, and humidity variations without dehydration. Thermal stability maintains properties intact within a range of −10°C to +60°C, thus covering the entire range of use on a human wrist. A crucial aspect for watchmaking: bio-rubber does not develop a characteristic odor and does not release volatile substances after the first few days, eliminating the typical inconvenience of natural rubber. The patina that forms over time is minimal; the color remains stable even under frequent sun exposure, avoiding the chromatic degradation that affects less noble elastomers. The material is hypoallergenic, free of natural latex and irritating additives, ideal for sensitive skin.

Use in Watch Straps

In handcrafted watch straps, bio-rubber fulfills distinct structural and aesthetic functions. Milano Straps uses bio-rubber in two main ways: as an elastic base underneath upper layers of vegetable leather or Cordura, or as the main covering material for sports and sporty-elegant models. In the first case, the strap features a vulcanized bio-rubber rib, usually 2-3 mm thick, which provides cushioning for wrist movements and dimensional stability during hot and cold conditions; over it, a calfskin or vegetable-tanned bovine leather lug is applied, creating a hybrid that combines the robustness of rubber with the aesthetic nobility of leather. In the second case, the strap is made entirely of bio-rubber, with refined finishes: geometric engravings that mimic the ribbing of leather, shaped edgings, decoupage lugs, and sometimes natural leather overlays applied with biocompatible glue. The stylistic compatibility of bio-rubber is broad: it naturally pairs with sports cases in titanium, 316L stainless steel, and modern quartz watches; it is ideal for divers and technical chronographs; it can be combined with navy blue or matte black leather dials without chromatic conflict. Unlike leather, which requires complementary tones, black, grey, or navy blue bio-rubber acts as a neutral that enhances dial readability. Compatible watch models include classic sports watches (Rolex Submariner, Tudor Black Bay, Omega Seamaster), technical wrist references (Breitling Superocean, IWC Aquatimer) and, in contemporary trends, also elegant chronographs with a 42-44 mm round case, where the bio-rubber strap aesthetically replaces metal, reducing weight and increasing thermal comfort. Milano Straps models available in bio-rubber range from the Athlete line (anatomical straps with a central cushion) to the Urbano line (thin 18-20 mm straps for elegant cases up to 38 mm).

Maintenance and Care

Bio-rubber, while being a robust material, benefits from targeted conservative measures. Routine cleaning: weekly clean with lukewarm water and mild non-abrasive soap, gently rubbing with a soft sponge; rinse thoroughly and dry with a microfiber cloth. Avoid concentrated alcohol-based products or acetone, which accelerate rubber aging. UV protection: although bio-rubber shows excellent UV stability, it is advisable to avoid prolonged and direct exposure to midday sun; store the strap in environments with diffused light when not worn. Storage: store the strap in a dry place, at temperatures between 15°C and 25°C, protected from excessive humidity and volatile substance vapors (gasoline, industrial solvents); do not expose to direct heat sources such as radiators. Controlled aging: unlike vegetable leather which develops a noble patina, bio-rubber maintains its original appearance even after years; any superficial micro-scratches are normal and do not compromise structural integrity. Annual maintenance: every twelve months of intense use, we recommend a revision at the Casati Milano atelier, where the attachments (pin buckle, deployment clasp) will be inspected, re-lubricated if necessary, and the surface protection renewed with a biocompatible water-repellent treatment. Repairs: tears and superficial lesions up to 5 mm can be sealed with specific elastomeric adhesive; more extensive damage requires replacement of the affected section, an operation performed by our master craftsmen. Bio-rubber does not decompose over time like natural rubber; its longevity typically extends to 8-10 years of daily use, far exceeding the durability of conventional elastomers.

Discover Milano Straps bio-rubber straps — Milanese craftsmanship, shipping in 48 hours. For a custom-made strap, visit the Casati Milano atelier in Via XX Settembre 15, Milan — by appointment.