Explicit formulas for $K$-types of a $({\frak g}; K)$ module, such as Blattner's formula, are well known. However, the formulas are often too complex to make the $K$-type structure transparent. In this note we make use of some ideas of Vogan linking the ‘edges’ of the set of $K$-types to a certain restriction map from ${\frak u}$ to ${\frak u} \cap {\frak t}$ cohomology. It is hoped that such ideas will lead to tighter control of the set of $K$-types.