Hi Santa Rosa. Sorry for the delay - We've been busy with the MOA rally. Legally, we say that you should follow the guidelines for max weight capacity that are stated by the manufacturer. So that equates to about 3 feathers... That said, many Micatech users (including ourselves) pack way more than we ever should into the top box. We've loaded them up and gone riding on some long and bumpy trails! Unless you're carrying bricks or dumbells you should be OK. Feel free to send us a photo of what you plan to pack and we'll take a closer look. Hope that helps!