The FiSER (filament stretching extensional rheometer) is based on the works by Sridhar et al. and Anna et al. In this instrument, a set of linear motors drive a fluid filament apart at an exponentially increasing velocity while measuring force and diameter as a function of time and position. By deforming at an exponentially increasing rate, a constant strain rate can be achieved in the samples (barring endplate flow limitations). This system can monitor the strain-dependent extensional viscosity, as well as stress decay following flow cessation. A detailed presentation on the various uses of filament stretching rheometry can be found on the MIT web site.