Informed by the participants' feedback to our initial design probe, we modified the design of the tactile overlay, and tested different combinations of materials to improve attacheability, legibility, and pressibility. Using a flat and thin sheet printed in flexible NinjaFlex as the base of the overlay can make the augmentation much easier to attach to the appliance interface with adhesive. The flexible material also made it much easier to press than using only PLA for the design probe.

While using NinjaFlex can improve attachability and pressability, it sometimes leaves undesired artifacts in the form of fine threads between Braille dots (think of melted cheese threads between pizza slices). These threads could reduce Braille legibility. One solution is to print Braille using solid material such as PLA (which we denote as Flex+PLA label). A problem that occurred with this design is that these Braille dots may become dislodged from the button surface over time, due to the combination of heterogeneous materials. Another solution for this is to print several layers of the button together with Braille dots in PLA, while printing the rest of the bottom layers in NinjaFlex, resulting in a larger contact area between the two materials to allow them to stick together nicely (which we denote as Flex+PLA cover).

We then performed a qualitative examination of the example applications with a blind individual (female, 24 years old, college student). In three different settings (i.e., pure NinjaFlex, Flex+PLA label, and Flex+PLA cover), the participant said all three testing material combinations were equally legible. Interestingly, she was most comfortable with reading the pure NinjaFlex version of the tactile overlay, despite the fine threads across dots. Unfortunately, both Flex+PLA label and Flex+PLA cover versions required her to press the button a lot harder to trigger the original interface. Overall, the NinjaFlex version of the tactile overlay had the best pressability and attachability among all material combinations we explored.