When you are exporting a DataRow value using a Stream Writer to formats like CSV, we write as dr[counter].ToString(). If this value starts with zero, Excel removes the leading zeroes (unless the column is formatted as text).

In order to fix this, we would need to manually write that as the following.

if(dr[i].ToString().StartsWith("0")) {      sw.Write(@"="""+dr[i]+@""""); } else { sw.Write(dr[i].ToString()); }