While the Brain Cell can be used on its own as a highly protective yet minimalist laptop case, it was designed to clip inside other larger TOM BIHN messenger bags, backpacks, and briefcases. Due to their different sizes, different bags will hold different Brain Cells. The following is a reference guide as to which sizes of Brain Cell fit in which bags:

Size 1 Brain Cell:
Empire Builder
Super Ego
Tri-Star

Size 2XL Brain Cell:
Super Ego

Size 2XXLT Brain Cell:
The 2XXLT can be used as a stand-alone case. It does not fit inside of any TOM BIHN bags.

Size 2M Brain Cell:
Super Ego

Size 2S Brain Cell:
Super Ego
Tri-Star

Size 3S Brain Cell:
Empire Builder
Brain Bag
Super Ego
Ego
Tri-Star

Size 4 Brain Cell:
Empire Builder
Zephyr
Brain Bag
ID
Super Ego
Ego
Western Flyer
Tri-Star

Size 4Z Brain Cell:
Empire Builder
Ego
Super Ego
Western Flyer
Tri-Star

Size 5 Brain Cell:
Empire Builder
Zephyr
Brain Bag
ID
Smart Alec
Super Ego
Ego
Imago
Western Flyer
Tri-Star

Size 6 Brain Cell:
Empire Builder
Zephyr
Brain Bag
ID
Super Ego
Ego
Western Flyer
Tri-Star

Size 6T Brain Cell:
Empire Builder
Zephyr
Brain Bag
ID
Smart Alec
Super Ego
Ego
Western Flyer
Tri-Star

Size 6X Brain Cell:
Empire Builder
Zephyr
Brain Bag
ID
Smart Alec
Super Ego
Ego
Western Flyer
Tri-Star

Size 6Z Brain Cell:
Empire Builder
Zephyr
ID
Super Ego
Ego
Western Flyer
Tri-Star