Double Wall Leak Proof Push Mug The Double Wall spill-proof mug has a capacity of 400ml. The mug is made of stainless steel, in the middle is a silicone ring allowing you to easily keep the mug without it slipping out of your hands. Because there is a pressure system in the cap you can open the cup with ease. The Double Wall Leak Proof push mug is available in four colors. The mug can be printed with your own design or logo. You can print your design or logo in up to five colors. You can also engrave your logo. The mug is produced BPA Free.