Using a zipper to close a bag is as easy as it gets. If you are at all concerned about the material, this model is made from nylon.
From Amazon
Port Designs Courchevel Clamshell Laptop/Notebook/Chromebook Professional Business Briefcase Sleeve Bag for 15 inch Windows/Macbook Student/Work Laptops - Black
Technoworld PLC
Port Designs 160512 notebook case 39.6 cm (15.6) Briefcase Black