What is disclosed is a conversion muntin for use on a glazing muntin to adapt the latter to support light-transmitting plastic panels, including a muntin cover element and a clamping strip. The cover element has a T-shaped configuration including a recessed stem portion and a pair of oppositely extending bearing arms. The stem is recessed to receive a portion of the glazing muntin and has a plurality of longitudinally-extending grooves formed therein. The clamping strip comprises a pair of elongated parallely-extending rails and a hood integrally formed therewith and adapted to receive the stem of the conversion muntin. The rails have oppositely-facing slightly-spaced lips which receive the conversion muntin stem therebetween and which engage said grooves to hold light-transmitting panels against the bearing arms of the conversion muntin.