dollar tree foam board

So recently I have been really into mini projects with tiny whoops. I recently built a mini RC paper airplane using a mini cheerson drone, and since then multiple aircraft using only two motors using differential with a fixed elevator. Examples of this would be flite tests video of making a mini...

This is probably in the wrong category. Oh well. My apologies. I have a plane designed by @RCSpaceFlight (can you tag people like on Twitter?) and I used it for my science fair project, which was: Which type of airfoil generates more lift: a KFm airfoil or a conventional airfoil? I ended up...

I watched the Flite Test Snowball episode and wondered why DTFB is not water resistant. My question is, is it the paper backing that doesn't like the water, or is it the actual foam, or both?

Hello, I live in Norway and can't get hold on Dollar tree foam boards. Would kapaline boards work? Their like foam covered with paper I think. Any other suggestions?