Caffeine is a Xanthine Alkaloid compound that is found in the leaves, beans and fruit of over 60 plants that acts as a stimulant in humans and also as a natural pesticide to certain insects. The 100% cotton t-shirts are black with the caffeine molecule printed on the front in white. The t-shirts are available in adult sizes from Small to XLarge+. See the size chart below as a guide.
| T-shirt size | Shoulder seam to hem (mm) | Width at underarm (mm) |
| Small | 665 | 440 |
| Medium | 690 | 490 |
| Large | 700 | 540 |
| X-Large | 740 | 595 |
| X-Large+ | 775 | 640 |
