an integral filter leaf assembly comprising microporous polymeric filter cloths heat - bonded to the apices of an undulating screen to form a strong unitary pressure resistant filter unit which essentially replaces filter leaf assemblies . the screen and felt sides of the filter cloths are preferably heat sealable thermoplastics , usually polypropylene to allow heat - bonding and heat - sealing of seams throughout for a unitary assembly strong in compression . outer filter coat is preferably porous expanded polytetrafluoroethylene . optionally , a circumferential stiff load - bearing frame may be enclosed within the assembly .