A dissolvable backing layer for use with transmucosal drug delivery devices includes a dissolvable hydrophilic region and a non-hydrophilic region that inhibits or slows migration of water, drugs, other active agents, or other molecules through the backing layer. The non-hydrophilic region can be a disperse phase of gaseous voids, droplets of a hydrophobic liquid, solid particles of a hydrophobic material, or water insoluble particles that are not necessarily hydrophobic. In the alternative, the non-hydrophilic region may comprise a continuous layer or component that is readily dispersible upon dissolving of the hydrophilic region. The backing layers may be used within any transmucosal delivery device used to delivery drugs or other active agents across a mucosal surface.