There is Foam Board and there is Foam Board

I wondered why my scratch builds were never as svelte as brother Bixlers, turns out its the New Zealand Foam Board is lost heavier that what's in the FT speed build kits

6mm Depron

That said i have found a New Zealand supplier of Deprom which is very light but need re-enforcement with tape typically

My local supply is around 30% heavier for an equivalent area the FT's. The card is much thicker and better attached to the core then the FT stuff, tah said its way heavier and not much stonger in any usefull measure as they both break if crashed.

It was particulary noticeable on my Fogey which never realy floated like Josh's and needed way more power than a 70 Watt 24Gram Blue Wonder, I needed 120 Watts to get it flying and the Coroplast version was even Heavier needing a 250 Watt motor.

My FTflyer speed build is around 270 grams ready to fly and floats like a butterfly

Some foam board from a speed build kit

6mm local supply