The Modular Shoe: Children's Footwear Designed for Developing Countries

KJ Lee, Alex Kowalski, Claire Usiak and Eli Zauner are students at Carnegie Mellon University.

Juan Carlos lives in the Dominican Republic in a town called Cabarete with his mother, Cassandra and his three sisters. His father left when Juan was six, and his mother began supporting her children by making shell jewelry and selling it to local tourists. Cassandra's relatives sometimes give the family clothes or money, but she is still having difficulty making ends meet. They live in a small shack made of tin sheets and wood in Barrio Blanco, a swampy plot owned by the government and inhabited by hundreds of squatters.

Juan is now nine and attends the nearest school, which he must walk three miles to and from each day. In addition, Juan often wanders around town to meet with friends or buy food. Before his father left, Juan always wore sandals when he went out. Now, his mother cannot afford to keep buying new sandals for Juan as he grows, and he walks everywhere on his bare feet. Juan doesn't mind walking on the road without shoes, but he has cut his foot several times on broken glass while walking through Barrio Blanco. Juan is normally very careful walking through the neighborhood, but when there is standing water on the ground Juan cannot see where he is stepping.

Recently, Juan cut his foot on a rusted sheet of tin that fell off the neighbor's house during a storm. Juan cannot walk to school with his injured foot, so he has decided to stop attending until his injury heals. Juan has been experiencing muscle spasms since he received the cut, which he told his mother. While Cassandra is worried about Juan, she does not know what is wrong and does not have the money or time to take Juan to the nearest hospital 30 miles away. Cassandra asked her brother to take Juan, and he agreed to do so in a few days. In the meantime, Juan's cut seems to be getting infected and the muscle spasms are worsening.

This scenario of Juan and Cassandra is not unusual. Children walking, running and playing barefoot is a common sight in many undeveloped countries across the globe. Over time their feet build up calluses that reduce the discomfort of walking on rugged terrain, but this does not protect these children from cutting and infecting their foot or contracting soil-transmitted diseases like hookworm and schistosomiasis. Many parents are unaware of these dangers and do not prioritize footwear for their children, or are simply unable to continually purchase new shoes for their children as they are outgrown or worn out. We set out to address these issues by creating affordable footwear that offers increased durability and adjustability to accommodate a child's growing foot.

In our design we sought to address a number of factors that had emerged from a survey we conducted with families in the Dominican Republic. Two features of primary importance were safety and security. Our design should allow children to feel independent by allowing them to explore and play without supervision, even on rough terrain. The children should also feel secure as they are protected from potential injuries and parasites. Similarly, children's families should feel secure knowing their children are sufficiently protected. Visual appeal also ranked very highly on the survey: the shoes must exhibit some personality to make them appealing to children who desire a sense of individuality. A design with visual appeal would also prompt children to encourage parents to make the purchasing decision even if they are unaware of the potential health risks of walking barefoot. At the same time the shoes must be reliable and durable.


We realized that a family's footwear costs could be reduced by creating a shoe a child can wear as he or she grows. The solution must enable children to continue moving in the same ways (e.g., walking, running, playing) and in new ways (explore new areas, play sports with shoes on). The last design factor was cost. The group of users we interviewed bought lower-quality flip-flops and replaced them as they wore out. To compete, our product needed to have a relatively low production cost.

Through multiple iterations, we created a shoe that grows with the child. We converged on a modular shoe design consisting of a toecap and a heelcap with links that can be inserted between the caps to lengthen the shoe. While this design created additional technical hurdles due to its multitude of components, it boasted superior qualities from a manufacturing cost and simplicity standpoint. From a technical standpoint, our challenge was to find the optimal balance between strength and comfort considering the shoe material and component geometry. A softer material increases comfort but also increases the likelihood components will snap out of position, break, or wear out over time. The geometry of the interlocking components faces a similar tradeoff between improved user experience and product functionality. Additionally, geometries must be designed to eliminate gaps between components during bending to keep dirt and debris from lodging in the gap -- and to prevent pinching the wearer's foot.

The basic design concept was refined and iterated through a combination of software modeling and simulation, and physical testing of prototypes. 3D printing technology was used to create molds of varying geometry; we filled those molds with a variety of resin and rubber-based materials to determine the best solution for the needs of our stakeholders. The design was also modeled virtually by creating 3D renderings of the concept sketches. We tested the virtual model by using a set of loading conditions that simulates the bending forces present during walking or running. These simulations identified structural weak points in our design and provided information about its overall strength.

Finally we arrived at the final design concept, a full-size shoe built of extruded polymer parts that slide together to adjust the size of the resulting shoe. Heel and toe pieces are built with appropriate strapping to secure the shoe to the user. By adding dyes of varying colors to different pieces, the shoe appeals aesthetically to children and their parents.


Product cost was a major factor in all design decisions as we recognized the financial constraints of our target consumer. Therefore the components were heavily designed for ease of manufacturability. The simple process begins by extruding three different profiles of rubber (or a soft plastic depending on the desired shoe performance), for each of the three unique components, which are cut to an appropriate length. These components are then stamped to create holes for the straps to be threaded through, and to potentially create a comfortable texture on the shoe's top and a gripping texture on its sole. The product could potentially be packed for shipping at this point, leaving assembly to occur at the point of sale or by the user, since the shoe is designed to be assembled and adjusted with ease. The minimal amount of equipment and dies reduces the startup capital required to produce the shoe. Further, it opens the potential for a localized manufacturing effort that can boost the local economy and reduce supply chain costs. The modular shoe is primarily competing with the flip flop or an equivalently inexpensive sandal. Our product seeks to differentiate by offering increased durability and adjustability that increases its lifetime. While the added complexity may result in a higher price point than the flip flop, the increased product life span offers a superior solution from a long-term cost efficiency perspective.

We still have a lot more iteration to go, but our modular shoe design has the potential to have a substantial impact on the health of children in undeveloped countries, such as Juan, who today walk without shoes.

--KJ Lee, Alex Kowalski, Claire Usiak and Eli Zauner

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