Solid　acids　have　been　widely　used　as　heterogeneous　catalysts　in　developing　green　and　sustainable　chemistry.　However,　it　remains　a　challenge　to　improve　the　mass　transport　properties　and　acid　strength　of　solid　acids　simultaneously.　Herein,　we　report　a　class　of　two　dimensional　(2D)　layered　hybrid　solid　acids　with　outstanding　mass　transfer　and　extremely　high　acid　strength　by　incorporating　sulfonated　polymers　in-between　montmorillonite　layers.　The　2D　layered　structure　and　broad　distribution　of　pore　sizes　allow　for　highly　efficient　mass　transport　of　substrate　molecules　into　and　out　of　the　solid　acids.　The　acid　strength　of　these　solid　acids　was　found　to　be　stronger　than　that　of　100%　H2SO4,　H3PW12O40　and　any　other　reported　solid　acids　to　date,　as　determined　by　1H　and　31P　solid-state　NMR.　These　2D　solid　acids　show　extraordinary　catalytic　performance　in　biomass　conversion　to　fuels,　superior　to　that　of　H3PW12O40,　HCl　and　H2SO4.　Theoretical　calculations　and　control　experiments　reveal　that　H-bond　based　interactions　between　the　polymer　and　montmorillonite　facilitate　the　unusually　high　acid　strengths　found　in　these　samples.　©　2019　The　Royal　Society　of　Chemistry.