You can set workbook.default_format_properties in 2 ways:

1. When you create workbook, set the 'options' parameter:

   wb = Workbook(options={'default_format_properties': {'font_name': ...., 'font_size': ....}})

2. After workbook created, before add_format(), set the 'default_format_properties' property:

   wb.default_format_properties = {'font_name': ...., 'font_size': ....}