metal
Steel; traditionally.
What the forget
If that's not the answer you're looking for then start acting like less of a dullard and explain better what you want to know.
Are they generally easy to break, because it's 1/4 of an inch thick and I just snapped it in half.
No, no they are not.I don't claim to know much about metalworking, but it sounds like it might just be a defective product. Depending on how you were using it and when you bought the file, it shouldn't be difficult to get a replacement.