Hi Ryan,
Could you please try using the following code snippets to set the postal codes with the leading zeros?
[C#]
//Number format to preserve the leading zeros
sheet.Range["A1:A2"].NumberFormat="00000";
//Import array of objects
sheet.ImportArray( arrInt, 1, 1, true );
Here is the sample for your reference:
ImportArrayBoder.zipPlease take a look at the sample above and let me know if you have any other questions.
Best Regards,
Melba