Lob offers a variety of form factors and related features that is accessible via the API or dashboard. 

Postcards & self-mailers

• 4x6" postcards
• 6x9" postcards
• 6x11" postcards
  
  
• 6x18" bifold self-mailers
• 12x9" bifold self-mailers
• 11x9" bifold self-mailers

Letters

• 8.5x11" letters
• Using Certified Mail & electronic return receipts
• Using Registered Mail
• Using card affix

Letter envelopes

• Standard outer envelopes (#10 and flat envelopes)
• Certified Mail envelopes (#10 envelopes)
• Return envelopes & tracking (#9 standard envelopes)
• Business reply envelopes (#9 standard envelopes)
• Custom outer envelopes (#10 envelopes)

Checks

• Adding a bank account
• Adding a signature
• Adding check pages