Among the polyol esters or ethers that may especially be mentioned are glycerol esters, poly-ethylene glycol esters, sorbitan esters, and mixtures thereof, for example glyceryl monoisostearate, such as the product sold under the name Peceol Isostearique by the company Gattefosse, PEG-8 isostearate, such as the product sold under the name Prisorine 3644 by the company Uniqema, sorbitan isostearate,