Abstract: A product employable in chemical working operations, for instance pipetting, where one or several devices are moved between, inserted into and withdrawn from a plurality of liquid containers arranged in a row, with the product preventing undesirable transfer of liquid between the containers. The product includes a layer of an absorbent material covering the openings into the liquid containers and closely engaging the devices to wipe off and clean their exteriors. The layer of absorbent material is fixed to a supporting layer provided with oval holes arranged to register with the openings into the liquid containers.