Biofilm mechanical stability is due to extracellular matrix, which fills the space between bacterial cells and binds them together. In this work we tested, how different expression of extracellular polimers in matrix in E. coli biofilms (PGA, curli, colanic acid) effects biofilm viscosity and viscoelasticity, as well as how it effects the resistance agains hydrogen peroxide. Additionally we tested the effect of adding water or detergents on biofilm viscosity. Results showed significant differences in viscosity and viscoelasticity among biofilms with different expression of extracellular polimers. The absence of proteinaceus curli had the greatest effect on mechanical properties. Overproducing of colanic acid significantly decreased viscosity, pseudoplasticity and also biofilm stability. In the absence of PGA, curli and colanic acid production, E. coli could still form a biofilm. Adding water or SDS solution significantly softened the biofims. The effect of hydrogen peroxide on bacterial cells was different among biofilms. MG1655 csrA mutant, which is overproducing PGA, showed the greatest susceptibility for hydrogen peroxide. Not all the cells in biofilm were killed by hydrogen peroxide.