We study the speci c heat of the x y model on lattices L L H with L H (i.e. on lattices representing a lm geometry) using the Cluster Monte{Carlo method. In the H {direction we apply Dirichlet boundary conditions so that the order parameter in the top and bottom layers is zero. We nd that our results for the speci c heat of various thickness size H collapse on the same universal scaling function. The extracted scaling function of the speci c heat is in good agreement with the experimentally determined universal scaling function using no free parameters. 64.60.Fr, 67.40.Kh The theory of second order phase transitions is based on the assumption that at temperatures close to the critical temperature T c there is only one dominating length scale associated with the critical behavior of the system, the correlation length. Because the correlation length diverges as the critical temperature is approached the microscopic details of the system become irrelevant for the exponents describing the most singular dependence of the thermodynamic functions on the reduced temperature t = T=T c 1. This intuitive picture has its foundation in the renormalization group treatment of second order phase transitions. Within the renormalization group treatment it becomes evident that the critical behavior can be divided into di erent universality classes which are characterized by a set of critical exponents.If the system is con ned in a nite geometry (e.g. a cubic or lm geometry) the nite{size scaling theory 1] is thought to describe well the behavior of the system at temperatures near T c . The intuitive idea behind the nite{size scaling theory is that nite{size e ects are observed when the bulk correlation length becomes of the order of the nite system size, i.e. for our case here the lm thickness H. For a physical quantity O this statement can be expressed as follows 2]:The dimensionless ratio on the left-hand-side of the above equation is a universal function f(x) of the dimensionless ratio x = H= , i.e. in our present work the lm thickness measured with respect to the correlation length. The function f depends on the boundary conditions and the geometry of the system. Liquid helium 4 He has been a very good ground both for testing nite-size scaling theory and measuring the critical exponents that go along with a second order phase transition in the case of a complex order parameter. Measurements of the super uid density 3] and speci c heat 4] on helium lms, however, fail to verify the nite-size scaling theory. Field theoretical calculations for the standard Landau{Ginzburg free energy functional in di erent geometries with Dirichlet boundary conditions have been carried out 5{8]. New speci c heat measurements 9] and also a reanalysis 10] of the old speci c heat data 4] show good agreement between the results of the calculations reported in Refs. 5{7] and those data. Furthermore, new experiments on liquid 4 He under microgravity conditions are planned 11] to examine the nite{size scaling properties of the speci c heat. The above ...