about 50 u00b0 f the polyol tubes were then opened and weighed into a metal mixing container about 100 grams of polyol blend are used the isocyanate from the cooled metal container is then immediately poured into the polyol and mixed with an air mixer with double propellers at 3000 rpm 39 s for 10 seconds the blend immediately begins to froth with the agitation and is then poured into an 8 u00d7 8 u00d7 4 inch box and allowed to foam because of the froth a cream time cannot be measured the foam has a 4 minute gel time and a 5 minute tack free time the foam is then allowed to cure for two days at room temperature the foam is then cut to samples suitable for measuring physical properties and is found to have a density of 2 14 pcf k factors are measured and found to be as follows this example illustrates the use of blowing agent in accordance with two preferred embodiments of the present invention namely the use of hfo 1234ze and hfo 1234 yf and the production of polystyrene foam a testing apparatus and protocol has been established as an aid to determining whether a specific blowing.