Props creation is an integral part of cosplay, as is sewing. A prop is not only a replica of a weapon, it can also be a more or less elaborate accessory.
Here are some examples below, the photos are currently of poor quality but I will try to give my props a shooting worthy of the name!
My favorite materials are insulation foam (expanding or sheets version) and EVA foam, I sometimes use thermoplastics like Worbla or Wonderflex but this is way too expensive and heavy for big props. Actually I am not interested on 3D printing, I am a craftsman not an ingineer 😉