An monolithic interlayer with high stiffness and when laminated into a glass panel, the glass panel exhibits good clarity, while maintaining the processability of a polyvinyl acetal, such as polyvinyl butyral resin used to make the monolithic interlayer. The monolithic interlayer comprising a polymer blend of: (A) polyvinyl acetal (e.g. PVB); and (B) one or more cellulose esters. The polymer blend increases the structural strength to the monolithic interlayer by increasing the E′ modulus of the monolithic interlayer while optionally maintaining good optical clarity.