DuoDERM Signal A Tapered-Edge CGF (Control Gel Formula) Hydrocolloid Dressing, Sterile. DuoDERM Signal dressing is an adhesive, tapered edge, modern hydrocolloid wound dressing with a change indicator. It incorporates a unique ConvaTec hydrocolloid formulation that distinguishes it from other hydrocolloid dressings. The adhesive hydrocolloid matrix and the outer film on DuoDERM Signal dressing are permeable by moisture vapour and provide an occlusive barrier against bacteria, viruses, dirt and water. DuoDERM Signal Dressing is indicated for the management of lightly to moderately exuding wounds.