Methods of protecting Pt(-alloy) particles against dissolution during fuel cell operation have recently gathered attention. Titania as a promising Pt catalyst support has its own built-in protection mechanism, called strong metal-support interaction (SMSI), which leads to encapsulation of metal particles. A high-coverage Pt particle film (approximated layer) with high oxygen reduction activity on the native oxide of metallic titanium has been heat treated in a hydrogen atmosphere. This treatment gave rise to its protection with a thin TiOx layer while Pt particle sintering or the destruction of the Pt structure was avoided. This unique behavior might originate from the structure of this approximate layer; i.e., contiguous patches of TiOx allow fast SMSI/encapsulation of the whole Pt structure before massive sintering or destruction can take place. Although the film was found to be covered by a 5.0 ± 0.1-nm TiOx overlayer, oxygen reduction with a mass activity of 26 ± 4 A gPt−1 could still be observed. Graphical AbstractOnce layer-like, always layer-like: Heat treatment of a very closely spaced Pt particle film leads to retention of this structure and formation of a TiOx overlayer by the strong metal-support interaction. In contrast, sparsely distributed Pt particles sinter under those conditions. This difference in behavior also has consequences on the oxygen reduction activity.