Encapsulation　of　expandable　graphite　(EG)　particles　by　organic　or　inorganic　shells　has　been　proved　to　efficiently　enhance　the　expandability　of　EG,　and　thus　to　improve　the　flame-retardant　efficiency　of　EG.　In　this　study,　magnesium　hydroxide　(MH)　nanosheets　were　utilized　to　fabricate　core-shell　EG@MH　flame-retardant　particles　through　a　heterocoagulation　method.　It　was　observed　that　after　the　encapsulation　by　MH　nanosheets,　the　edges　of　the　char　residue　of　the　EG　layer　were　sealed　after　combustion,　which　contributed　to　the　enhancement　of　expandability.　The　expansion　volume　of　EG@MH　increased　dramatically　to　456　mL/g,　in　contrast　to　338　mL/g　for　pure　EG.　By　incorporating　11.5　wt　%　of　flame-retardant　particles,　polyurethane　foam　containing　EG@MH　(here　PU-EG@MH)　displayed　excellent　flame　retardancy.　Compared　with　the　physically　mixed　sample,　PU-EG+MH,　the　limiting　oxygen　index　value　for　the　PU-EG@MH　sample　increased　from　29.8%　to　32.6%.　Furthermore,　the　shell　of　MH　nanosheets　was　beneficial　for　improving　the　interfacial　adherence　between　EG　and　the　rigid　polyurethane　foam　(RPUF)　matrix,　due　to　the　reaction　between　isocyanate　functional　groups　and　MH.　The　cell　structure　and　storage　modulus　of　PU-EG@MH　were　improved.　In　other　words,　the　shell　of　MH　nanosheets　successfully　improved　the　flame-retardant　efficiency　and　enhanced　the　interface　adhesion　between　EG　and　the　matrix.　(c)　2018　Wiley　Periodicals,　Inc.