E.V.A, THE BEGINNING OF THE END? Part 1 : INDUSTRY REMINDER

Ethylene-vinyl acetate (EVA), also known as poly(ethylene-vinyl acetate) (PEVA), is the copolymer of ethylene and vinyl acetate. The weight percent vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene.

EVA is an elastomeric polymer that produces materials which are "rubber-like" in softness and flexibility. The material has good clarity and gloss, low-temperature toughness, stress-crack resistance, hot-melt adhesive waterproof properties, and resistance to UV radiation. EVA has a distinctive vinegar-like odor and is competitive with Polyurethane in footwear applications. (source Wikipedia)

Footwear industry, back to the mid 70's envisioned the EVA Material as a solution in order to improve the overall comfort of active footwear. The first generations of running shoes fitted with EVA looked pretty much like the picture above. Mizuno Sky Race 1995 

The upper were generally a Mocassin construction, lasted in the forefoot over a dye-cut EVA Midsole and rubber outsole. The down-side of the cutting process lies in its binary look. An austere sand paper look.

In the same decade, I have been told That Brooks Sport were the very first company to compress- mold the EVA instead of the common dye-cut process. 

Unfortunately, I cannot prove myself right as I am still looking for the proven facts and Brooks doesn't seem to communicate this part of their history. 

This molding process opened a vast world of creativity in term of function and design. The heat of the mold melted the sand paper looked surface and turned it into a thin soft skin. We suddenly could create shapes and lines easily.

The other main material player of the 70's and 80's is the POLYURETHANE full sole as for the Adidas zx 8000 produced in 1988/89. 

The POLYURETHANE had fantastic characteristics of shape memory, due to its formula. The EVA is still generally loosing its dampening quality way faster than POLYURETHANE does. 

EVA has a minor density which makes it by far lighter than POLYURETHANE of that era. The Other downside of the POLYURETHANE were found in its weak resistance in keeping its original color (yellowing effect) and poor performance in Hydrolysis. Most of you might remember the midsoles breaking and powdering.

Once the compression molding process democratized, most Brands were sometimes combining EVA and POLYURETHANE in order to get the best of the two materials, mainly for functional reasons. 

In this case, Nike with the Nike Pegasus 1988 took the advantage of EVA for an overall lighter product at the forefoot. The POLYURETHANE guaranteed a long lasting heel cushioning. The air wedge embedding process also needed a POLYURETHANE environment until late year 2000.

1987 showed an other design/functional approach: a Stabilizer chassis called RSD. The Molding process of either EVA or POLYURETHANE (in this case) could fit with precision, different quality of Polymers together. Adidas ZX 820 Women.

Here is Another solution found at Adidas in order to improve the durable performance of EVA. 

A web was bonded over the EVA from top to the side of the midsole for a trampoline effect.

The story doesn't tell if this idea inspired brand SAUCONY for their GRID system, or vice versa? 

In a world of technologies, it is interesting to see how foams, in particular EVA and POLYURETHANE became a kind of a given standard to the average customer.  Here the nike air Max 1994.

Lets take the thought further, I would even see those foams as a platform of other visible technologies that became over time the more valuable additive systems and more precious in people's mind than the foam itself.  

I think it is an unfair lack of recognition to the foam. 

The visible air Max unit and its little sister the non visible forefoot air wedge were only additive richness and function to the product, never the reason why the shoe was more comfortable. 

until Adidas spring blade 2012 and Nike Vapor max 2016 , no active shoe cushioning system was available without foam.

Another example of foam being an interface in between the foot and the ground. Reebok Opus 3d foam 1997. 

Reebok gave a durability challenge to the EVA foam by removing the Rubber and claiming the foam is durable enough to withstand friction. 

But the stars of the picture are the Graphlite plate made of composite fibers and the unexpected shaped upper. 

Complex Mold processes, proved how the EVA is somehow flexible in combination of different characteristics. 

This Puma offers 5 variety of EVA within the same midsole, the M cell being bouncy, the O cell being cushy, a medial post being harder the white overall foam being medium and the ISS co molded plate for midfoot stability.

This shoe images the end of an era, the Lego blocks answering biomechanics in selected areas have been the pinnacle of the EVA combined evolution, far more complex than the dye-cut process. 

One question Though, was it better?