When you insert a dielectric material (like glass) between the plates, the permittivity ε increases because the dielectric constant k of glass is greater than that of air or vacuum. The new capacitance when a dielectric is inserted is given 

C′ = \(\frac{\text{kεoA}}{\text{d}}\)

where k is the dielectric constant of the glass, and ε\(_0\) is the permittivity of free space.

Since k >1 for glass, inserting it increases the capacitance:

C ′ = kC

Thus, with the glass block inserted, the capacitance C′ will be greater than the original capacitance C.