Abstract: An expandable in-ear device for being custom fitted in-situ into the ear canal and cavum concha of an individual. The device includes a core-form with a platform section and a nipple section being integral to and extending from a proximal end of the same for engaging the canal, a sound bore extending from a proximal end of the nipple section to a distal end of the platform section for conducting sound from the environment to inside the ear canal. A stretchable sheath is integral to and freely extends away from the proximal end of the nipple section in an unfolded configuration of the device. The sheath is essentially a replication of the shape of the core-form and has an opening adapted for assuming the distal end of the platform section. The sheath is adapted to be folded inside-out over the core-form, substantially assume the same and define an in-between region therebetween in a folded configuration of said device.