Faraday cage basics

The other day at work, a higher ranked engineer claimed that my faraday cage won't work because it's not an actual "cage" but solid a metal (Al) box. I felt stupid asking him why for the third time, so now I'm posting here: Is there really any physical argument that says that it must be a cage (made of threads) and not a solid box?

I found the following link which appears to be helpful: http://www.physlink.com/education/askexperts/ae176.cfm.
BTW I have entered a large Faraday room made of 1/2 inch lead in which a "Giant" Tesla coil was set to work. The room provided an effective shield at those frequencies.

Hi Ulrik,
These is a joke with "beginners/news" ...
Maybe you are heared over another tradition for a full beginner in a workshop; the older will he send to the "maestro" for some "fat for files" , or in some languages is phase angle or phase degree is to say/use as: "phase nail"_of course must bring the new person/student a half kg of "phase nail" from corporates mechanical parts stock or from some dealer ...
Btw: a shild is so better as thighter/fuller material is, as "poor mystic" mentioned too.
K.