[Mike K]

Interesting suggestions . Apparently there is another way of doing it . With wide seats , its difficult to achieve a nice level cut by hand with a knife ...

You make up two templates , the shape you want . Find a old electric radiator and strip out the nichrome wire from the element .

You fix the wire to a suitable frame or holder ,it must take the heat so metal or ceramic posts are ideal .

You situate the foam between the two templates , run a current through the wire ( 12 or 24 volt will suffice , but may require some experimentation to get the correct heat range ) until its nice and hot, then drag the wire over the templates and it will follow the shape .. and cut the foam.

I think Rc model aircraft people do this method when making foam wings from styrofoam.