filler in engine mounts what to use ?

I hear you can put filler or something in your engine mounts to make them more stiff whats the best thing to use ?

some people use sikaflex

i used tigerseal it worked real well 4 a while, but my mounts were floppy as fuck 2 start off with but if ur mounts are ok it should do the trick. its just u need 2 remove ur mounts and allow them 2 dry it took me a few days even with the odd blast with a heat gun

thanks, my mounts are all out so ill buy some soon my engine wont be in for about 3 weeks so i got time