Both Squadron and Tamiya Putty were meant for plastic models, so styrene is their intended material for use. Just don’t apply it too thick. I use Bondo on a variety of materials, but usually not on plastic. But it should be fine. I know Bondo Spot Putty will crack if applied too thick, and assume the others might. I’ve always applied Squadron or Tamiya sparingly. I just build up the application where I need a thicker fill.

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Lee Reep
NAR 55948

Projects: Semroc Saturn 1B, Ken Foss Designs Mini Satellite Interceptor
In the Paint Shop: Nothing! Too cold!
Launch-Ready: Farside-X, Maxi Honest John, Super Scamp