In this work we consider an important problem of multiproduct batch plants which is the uncertainty in process parameter values and in product demands. This context raises the Flexibility problem. It has been defined as the need to size the plant such that this guarantees that all constraints are satisfied for any value of the parameters during the process operation. Therefore, this problem demands consideration of two opposite goals : maximum flexibility vs. minimum cost. It can be approached as a bicriterion optimization problem. Such a problem yields an infinite set of pareto optimal solutions that force only one arbitrary decision to obtain the solution. However, this decision involves a set of factors that should be considered individually. Moreover, it must be borne in mind that it is only the investor who will take this decision. That is why, if the problem requires a subjective decision to be taken, it is important that at least an effort be made to offer an appropriate frame to support the decision. The fuzzy sets are a mathematical tool to represent vagueness in everyday life. There is much evidence nowadays that fuzzy approaches to real problems are often a good alternative to more familiar schemes. Thus, in this work we will use them to approach the problem in the terms formulated above. Then, we present an algorithm based on this strategy.