Tactile materials are powerful teaching aids for students with visual impairments (VIs). To design these materials, designers must use modeling applications, which have high learning curves and rely on visual feedback. Today, Orientation and Mobility (O&M) specialists and teachers are often responsible for designing these materials. However, most of them do not have professional modeling skills, and many are visually impaired themselves. To address this issue, we designed Molder, an accessible design tool for interactive tactile maps, an important type of tactile materials that can help students learn O&M skills. A designer uses Molder to design a map using tangible input techniques, and Molder provides auditory feedback and high-contrast visual feedback. We evaluated Molder with 12 participants (8 with VIs, 4 sighted). After a 30-minute training session, the participants were all able to use Molder to design maps with customized tactile and interactive information.