A4 Trifold is the perfect size. Compatible with bills (receipt, invoice, sales status, etc.). Compatible with inkjet printers, digital printers, and perforated printing machines. Please note that the laser printer may have some wrinkles depending on the model. A4-format tri-fold and 3-section storage window layout to ensure the address is visible. The envelopes are double sided tape on the lid for a smooth seal after sealing the paper. In addition, since the window is made of glass paper, it can be recycled without sorting, it is environmentally friendly. We created an ecology and economy concept.