In this paper we use the notion of weak compositions to obtain polynomial kernelization lower-bounds for several natural parameterized problems. Let d ≥ 2 be some constant and let L 1 , L 2 ⊆ {0, 1} * × N be two parameterized problems where the unparameterized version of L 1 is NP-hard. Assuming coNP ⊆ NP/poly, our framework essentially states that composing t L 1 -instances each with parameter k, to an L 2 -instance with parame-We show two examples of weak composition and derive polynomial kernelization lower bounds for d-Bipartite Regular Perfect Code and d-Dimensional Matching, parameterized by the solution size k. By reduction, using linear parameter transformations, we then derive the following lower-bounds for kernel sizes when the parameter is the solution size k (assuming coNP ⊆ NP/poly):Cover, Hitting Set with d-Bounded Occurrences, and Exact Hitting Set with dBounded Occurrences have no kernels of size O(k d−3−ε ) for any ε > 0.• K d Packing and Induced K 1,d Packing have no kernels of size O(k d−4−ε ) for any ε > 0.• Our results give a negative answer to an open question raised by Dom, Lokshtanov, and * The full version of this paper can be found at [21].† Contact: Max Plank Institute for Informatics, Germany, Email: hermelin@mpi-inf.mpg.de.‡ Contact: University of Wisconsin-Madison, USA, Email: xiwu@cs.wisc.edu.Work done during the research visit at Max Planck Institute for Informatics, Germany. Research partially supported by NSF grant 1017597, NSFC grant 60973026, the Shanghai Leading Academic Discipline Project (no. B114), and the Shanghai Committee of Science and Technology (nos. 08DZ2271800 and 09DZ2272800).Saurabh [ICALP2009] regarding the existence of uniform polynomial kernels for the problems above. All our lower bounds transfer automatically to compression lower bounds, a notion defined by Harnik and Naor [SICOMP2010] to study the compressibility of NP instances with cryptographic applications. We believe weak composition can be used to obtain polynomial kernelization lower bounds for other interesting parameterized problems.In the last part of the paper we strengthen previously known super-polynomial kernelization lower bounds to super-quasi-polynomial lower bounds, by showing that quasi-polynomial kernels for compositional NP-hard parameterized problems implies the collapse of the exponential hierarchy. These bounds hold even the kernelization algorithms are allowed to run in quasipolynomial time.