These giant pumpkins are made out of styrofoam and they look realistic.

Insert skewers to hold them together temporarily while the foam dries.

Coat the pumpkin with primer, then let it dry, and paint it orange.

Easy DIY Giant Foam Pumpkin Tutorial

Image credit: Hollywood Haunter via YouTube

Easy DIY Giant Foam Pumpkin Tutorial

Easy To Make DIY Giant Foam Pumpkin

How To Make DIY Giant Foam Pumpkin