Surfacing > Creating Advanced Surface Features > Creating a Blended Surface from a File > About Creating a Blended Surface from a File
  
About Creating a Blended Surface from a File
You can create a blended surface by importing curves from a file in the .ibl format.
As the data for the surface feature is stored in the part as well as in the file, even if the file is deleted from the disk, you can still modify the feature.