Wedge heel shoes have been a necessary style for women’s shoes. However, because of the shape of the wedge heels, the shoes will become very heavy if we use rubber to make the wedge heels. That is why most shoemakers use plastic materials to make the main body of the wedge heels and attach thin rubber outsoles to the heels to increase the durability.  Johnny Yu, the founder of Dr. Sole, had been longing for a light, durable, and one-body molded wedge heels since he started making soles when he was 15 years old. In order to achieve this goal, using “rubber sponge” seemed to be the only method. The so-called “rubber sponge” is created by adding blowing agent into the rubber during the production process. The blowing agent lowers the density of the rubber and makes the rubber expand, making the “rubber sponge” softer and lighter than the pure rubber. However, the tradeoff is that the durability of rubber sponge is not as significant as pure rubber. The most difficult aspect of creating the rubber sponge to produce the wedge heels is controlling the expanded ratio. 

     Simply stated, the process of making rubber sole is to put the rubber material into a mold, and then “bake” the rubber to shape it into the exact form of the mold. When we take the rubber out of the mold, it becomes the soles and the shape and the size are exactly the same shape and size of the mold. However, once we add the blowing agent into the rubber, everything is different. After taken out from the mold, the rubber sponge gets expanded first, and then shrinks  again when it is cooled down. Hence, the rubber sponge soles are usually bigger than the mold. If we add more blowing agent into the rubber material, the rubber sponge soles will get bigger, sometimes several times bigger (the soles become softer and lighter, but, on the other hand, the durability will be compromised). That’s also why the formula plays a very important role in making rubber sponge sole.

      For these reasons, there are hardly any other sole makers using the rubber sponge to manufacture the “last-fitted soles” like the wedge heels. The “last-fitted soles,” as implied by the name, are soles that must perfectly fit the shape of the bottom of the last. That is to say, they must be one-shape-molded and there must be different soles for each size respectively so that every sole can be perfectly glued to the last and uppers during the shoemaking process. As a result, sole makers always use the materials that are easier to predict and control their size and shape, such as rubber or plastics, to produce the “last-fitted soles.” 
    
     In order to use the rubber sponge to produce the wedge heels, Johnny realized that “1:1 expansion” is the only way to ensure that the size of every rubber sponge sole will be as same as the mold. “1:1 expansion” means that when the rubber sponge soles are taken out of the mold (they expand first, and then, shrink a little bit when cooled down), they will become exactly as same as the shape and size of the mold (in the same way, if the soles become twice bigger than the mold after cooled down, it is so-called “1:2 expansion”). As previously mentioned, the adjustment of the formula plays an extremely important role in manufacturing of “1:1 expansion” rubber sponge soles because it won’t be able to achieve “1:1 expansion” if the formula has been changed, even the slightest bit. 

     After many trials and errors for several years, “RBS rubber sponge wedge heels” finally launched. All the drawbacks of traditional wedge heels were modified: they are lighter and more flexible than the rubber wedge heels, and they are one-body-molded; there is no need to attach a thin rubber outsole to improve the durability and traction. Most importantly, RBS rubber sponge wedge heels enhance the functionality of the wedge heels by offering the softness and comfort for the front thinner parts and a stable support for heels. Owing to these advantages, RBS rubber sponge wedge heels are Johnny’s favorite product ever. He always said that it is really a dream come true that he could successfully developed the RBS rubber sponge wedge heels, a product that he had been dreamed about since he was 15 years old. 
One-Body Molded Wedge Heels

     RBS rubber sponge wedge heels have been favored and used by many European, American, and Japanese brands since they were launched. This excellent product, Dr. Sole’s favorite product, has become another patented product.