  As was shown by Aharony, Hanany and Kol and independently by Sen, type IIB
string theory admits configurations where strings of different charges (p_i,
q_i) form so-called string networks. We argue that these networks blow up into
"supersheets": supersymmetric spinning cylindrical D3-branes carrying electric
and magnetic fluxes. These supersheets are three-dimensional generalizations of
the supertubes that were constructed by Mateos and Townsend. We calculate the
mass of both systems for arbitrary values of the parameters and find exact
agreement.
