The Sartocheck 4 plus bag tester uses the pressure-drop technology to allow pre-use testing of single-use bioreactors, including tubing. The bag tester is capable of detecting leaks that might have been caused by operator handling errors upon installation of a bioreactor, which can reduce the risk of filling a defective single-use bioreactor with expensive cell cultures. Single-use Biostat CultiBag STR bioreactors with working volumes of 50 liters and 200 liters can be tested by this new system. The system’s fleece technology prevents direct contact between the bag and the smooth stainless steel surface of the holder, reducing heat transfer and preventing the masking of any potential pinholes.