A sterile, implantable, non-bioabsorbable synthetic material (e.g., hydrophilic polyacrylamide gel) intended for submucosal injection in the urinary tract (urethra, urinary bladder, and/or distal ureter) to add volume by serving as a space-occupying supplement (bulking agent) to the intercellular matrix of connective tissue in the treatment of stress urinary incontinence (SUI) and/or vesicoureteral reflux (VUR). It is in the form of a gel material typically preloaded in a disposable syringe and is implanted using an endoscope and/or other dedicated instruments.