What natural rubber is
Natural rubber (NR) is polyisoprene harvested as latex from the rubber tree, Hevea brasiliensis, mostly in Southeast Asia. Its long, flexible polymer chains give it high elasticity, tear strength and a slightly tacky surface. Most performance outsoles blend NR with synthetic rubbers; outsoles described as natural rubber use NR as the main or only base polymer.
How natural rubber outsoles are made
- Tapping and processing — Latex is collected from the tree, coagulated, washed and dried into sheets or blocks.
- Compounding — NR is mixed with fillers, oils and a sulfur cure system.
- Molding and vulcanization — Blanks are vulcanized in a heated mold, as with other rubber outsoles.
- Crepe soles are a special case — latex is coagulated and pressed into thin, crinkled sheets that are layered into a sole, often with little or no vulcanization. This gives the soft, springy feel and distinctive look of classic crepe-soled shoes.
Grip: 8 / 8, Max
Soft natural rubber conforms closely to the surface and has a naturally tacky feel, which gives excellent grip on smooth, dry surfaces and indoor floors. It also stays flexible at low temperatures, so it keeps more of its grip in the cold than many synthetic compounds. On wet surfaces, tread design and filler choice still decide the result.
Flex: 8 / 8, Max
Natural rubber is highly elastic and bends repeatedly without cracking. Outsoles feel supple from the first wear and move easily with the foot, which suits casual, indoor and minimalist footwear.
Abrasion: 4 / 8, Medium
Soft NR compounds wear faster than SBR, BR or carbon-filled compounds, with higher volume loss in ISO 4649 testing. Natural rubber also has poor resistance to oils, fuels and high heat, so it does not suit outsoles that must meet oil resistance (FO) or heat resistance (HRO) requirements in EN ISO 20345:2022 on its own. Blending with synthetic rubbers is the usual way to keep most of its grip while extending wear life.
Where natural rubber is used
- Casual and heritage footwear — gum soles and crepe soles with a distinctive look and feel.
- Indoor and court shoes — grippy, non-marking compounds for smooth floors.
- Minimalist and barefoot shoes — thin, flexible outsoles with good ground feel.
- Cold-weather footwear — compounds that stay flexible and grippy at low temperatures.
Designing with natural rubber
Use natural rubber when grip, flex and feel lead the brief, and wear is moderate. Blend or zone it when the outsole must last or resist oil and heat.
- Blend NR with SBR or BR to extend wear life while keeping good grip.
- Avoid pure NR outsoles in kitchens, workshops and other oily environments.
- Use UV and ozone protection in the compound; NR can crack with long sun exposure.
- Ask suppliers about plantation sourcing and certification if sustainability is part of the product story.