It sounds as though an INDEX/MATCH approach should suffice.

It's not clear if the values should always be an exact match or find last value on axis <= criteria (this we will assume)

'Tab 1'!C2:
=INDEX('Tab 2'!$B$2:$M$11,MATCH($A2,'Tab 2'!$A$2:$A$11),MATCH($B2,'Tab 2'!$B$1:$M$1))

where A2 holds weight and B2 holds mould cavity