We consider robust variants of the bin packing problem with uncertain item sizes. Specifically we consider two uncertainty sets previously studied in the literature: budgeted uncertainty (the U Γ model) in which at most Γ items deviate, each reaching its peak value, while other items assume their nominal values. The second uncertainty set, the U Ω model, bounds the total amount of deviation in each scenario. We show that a variant of the next-fit-decreasing algorithm is a 2 approximation for the U Ω model, and another variant of this algorithm is a 2Γ approximation for the U Γ model. Unlike the classical bin packing problem, it is shown that (unless P = N P) no asymptotic approximation scheme exists for the U Γ model, already for Γ = 1. This motivates the question of the existence of a constant approximation factor algorithm for the U Γ model. Our main result is to answer this question by proving a (polynomial-time) 4.5 approximation algorithm, based on a dynamic-programming approach.