The distance between two parallel tangents to a circle is equal to twice the radius of the circle.
Given the radius of the circle is 4 cm, the distance between the two parallel tangents is:
\[
\text{Distance} = 2 \times \text{radius} = 2 \times 4 = 8 \, \text{cm}
\]
Thus, the distance between the two parallel tangents is 8 cm.