Library sizes

I made some tests. I wrote code direclty in the IDE window, I get 5440 bytes total size. If I make a library out of it and instantiate the class in the IDE window the code grows 200 bytes. If I preinstantiate an instance in the library, I save 100 bytes. Wtf? What is that 100-200 extra bytes anyway? Anyone have any other tips on how to make libraries smaller? Can I make a C library instead?