In this step, water is gradually removed from the sample and replaced by an organic solvent such as ethanol, propylene oxide or acetone. These solvents have a lower surface tension and substitute the water while maintaining the biological structure. Without this solvent replacement, strong drying artifacts would result from shrinkage of the sample. The dehydration step is also important because the resin (e.g. Epon) cannot be mixed with water for embedding and needs to be mixed with solvents for infiltration.