The present invention relates to means for covering one or more sample(s) that are suitable to avoid or minimize evaporation and/or condensation of any vaporizable substance that may be present in the sample(s) or reaction mixture(s), in particular evaporation of substance at the fringes of a vessel or an array of vessels or condensation of said substance on the lid of a reaction vessel or a plate/block containing the sample(s) and/or the means for covering. This is achieved by providing a device comprising, among others, a force distribution unit that comprises at least one medium or material that is unable to withstand a static shear stress and deforms continuously under the action of a shear force. In a preferred embodiment, this medium or material is a gas, a shear force.