Netzung in this context translates as 'wetting', which means the property of forming a more or less uniform film of a liquid on the surface of a (usually solid) substrate. and Lack is a coating such as a varnish or paint.
Substances that interfere with or hinder wetting by a coating material can be described (in German) as lacknetzungsstörend.

Perhaps you could say that the material is free of wetting inhibitors or substances that inhibit wetting.

sample refs:

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Heavy Duty Marine and Industrial Chemical Products, Alpha Marine ...
A concentrated acid, with an acid stable wetting inhibitor and glycol grease ... Coatings. ALPHACOAT. A superior corrosion inhibitor for all metal or ...
www.alphamarinesolutions.com/chemicals.htm

Process for Preparing Polyisobutyl-Substituted Cyclohexanols - Patents
For surface modifications in the form of coatings, on the other hand, ...... dispersant, adhesion promoter, binder, wetting agent or wetting inhibitor. ...
www.faqs.org/patents/app/20080221370