Does __attribute__((__packed__)) aplies to types or variables?

Suppose that I have a declaration:

struct __attribute__((__packed__)) foo {
  char ch;
  int number;
};

Will be any variable of this type be packed?

The real world thing is: I have a code that come up from 8bit world,
with a lot of lots of chained structures that are transferred throght
some radio frequence module, I need be sure that all this structs have
no padding so that they can be transferred as they are to radio. To
achieve this I've
putted __attribute__((__packed__)) to every struct and inner struct
that are sended through RF,
but I read at some StackOverflow post that packed attribute aplies to
variables not to types,
so I came here ask to experts. Is that true?

At gcc manual I found Type Attributes and Variable attributes, so I'm
assuming both exists how differentiate from one to another?

Regards,

-- 
"Do or do not. There is no try"
  Yoda Master