## 1 Background and Introduction  
Electronic textiles (e-textiles) can be categorized as wearable technology, finding applications in many appliances, such as interactive clothing or wearable sensors for sports and healthcare. [PERSON] [1] mentioned in 1964 how \"the computer is the most extraordinary of man's technological clothing\" by suggesting that it can be \"extension of our nervous-system\". [PERSON] [2] discussed further in 1991, where the author stated \"the most profound technologies are those that disappear\". Both authors' common idea was how technology \"weaves itself into the fabric of everyday life until they are indistinguishable from it\". Smart clothing possibilities were already proposed and discussed with some examples (e.g., shoe to measure impact on the leg) by [PERSON] and MIT late 20 th century [3; 4; 5]. The main idea of wearable computing was to bring everyday technology, such as cellphone, personal music system (e.g., Walkman, CD-player), etc., to a single unit, possibly improving personal health monitoring with sensors (e.g., heart rate check, respiration rate, etc.) and decreasing crime by being \"a seamless extension of the body and mind\" [5]. Refining from that, now, smart textiles (including e-textiles) are most commonly defined as \"fabrics or apparel products that contain technologies, which sense and react to the conditions of the environment they are exposed to, thus allowing the wearer to experience increased functionality\" [6]. [PERSON] and [PERSON] [7] in their 1997 conference proceedings bring out how metal-based yarns have been used in clothing for centuries already for decorative purposes. With computers growing smaller towards the end of the 20 th century, these conductive textiles could also be used as sensors and powering and data distribution tracks. The authors also create demonstrators by soldering surface-mount components on conductive (copper) textiles or using conductive textiles as capacitive sensors. Moreover, the same work is enhanced a few years later by embroidery technique where in several e-textile demonstrators mainly only textile-based materials were used [8]. In the early 2000s, [PERSON] and [PERSON] together with SparkFun Electronics created The Lilypad Arduino--a toolkit that could help to develop and prototype e-textiles quickly and efficiently [9; 10; 11]. The toolkit included easily sewable sensors and microcontroller(s), which simplified the e-textile prototype creations extensively. However, as the core material of e-textiles is, and should be, textile, these applications will need to be washed regularly by the user. This could cause reduced reliability and shortened lifespan of products and is one of the main shortcomings for entering the mass-market. Earlier works describe how the electronics could be removed (e.g., with the help of snap buttons) [7]. However, as wearable computing or wearables have developed extremely fast during the last years (smartwatches and smartphones), the end-users will be expecting easy-maintenance and reliability also from textile-based wearables. That could be achieved if no or a minimum amount of parts are needed to be removed for washing and everyday maintenance. In more recent literature, different materials (e.g., conductive threads and structured copper foils) are tested with various encapsulation methods. The research towards washability is mostly based on the ISO 6330 (International Organization for Standardization) washing procedure [12]. However, details about the used materials and integration methods are often left out. [PERSON] et al., 2017, integrated LEDs with various types of conductive threads onto fabric, encapsulating it with thermoplastic polyurethane (TPU) film and comparing those results with samples without encapsulation. The study proved the value of TPU encapsulation as a method for keeping the electrical resistance of the tracks within acceptable values [13]. However, only one TPU film was used with one layering method.