Aspects of the invention include preforms used to be formed into an immobilizer for use with a patient. The preform includes a preform member that is formed from a thermoplastic material and a filler material. The preform member is relatively rigid at a first temperature and formable at an elevated second temperature. The preform member is opaque at the first and second temperatures. The preform also includes at least one indicator associated with the preform member. The at least one indicator is formed from a thermoplastic material and is opaque at the first temperature and translucent at the second temperature. The at least one indicator can provide a visual indication of readiness to form the preform into the immobilizer upon heating the preform member to the second temperature at which the indicator is translucent.
