The most facile way to control properties at a fluid-fluid interface is to control the concentration at the interface. The concentration at the interface can be controlled by interfacial adsorption amount of functionalized materials or substances such as surface-active molecules, ions, polymers. A ultra-thin two-dimensional interface can be saturated with only a small amount of material compared to the three-dimensional bulk space. These properties can be exploited for applications that require both percolation and softness. With this in mind, we are working to develop materials for stretchable electronics that possess high electrical and/or thermal conductivity while also being flexible. In a typical three-dimensional system, the flowability and conductivity cannot be achieved simultaneously due to the their trade-off relationship. However, for two-dimensional fluid-fluid interface system, percolation can be easily achieved with only a small amount of functionalized material while maintaining the flowability of the liquid. This is expected to enable the synthesis of colloidal-based conductive materials that have high conductive properties along interfaces while also being flexible.