The ornamental design for external thermal insulation composite panel, as shown and described.
1. External thermal insulation composite panel
1.1 : Top-left perspective view
1.2 : Bottom-right perspective view
1.3 : Top
1.4 : Right
1.5 : Back
1.6 : Front
1.7 : Left
The marble chips pattern is a symbolic marking of the decorative and protective natural/artificial stone-based coating and does not form part of the claimed design; the insulation material pattern is symbolic and does not form part of the claimed design; reproduction.