Looking for linear non polar compound which is used heavily due to its boiling or melting temperature or its density
A possible answer is n-octane,



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for what it


consists of linear organic molecules (vide infra)
has a boiling point of about $125\,\pu{^\circ{}C}$ / $257\,\pu{^\circ{}F}$
is a hydrocarbon you either find in, or generate from natural oil


A bit on the n in n-octane:  This is a shorthand for normal, because the carbon atoms are consecutively bound to each other in an open chain.  Which is not the same as if they would form branched molecules, then denoted iso-octane.  A prominent iso-octane (iso as in isomer, i.e. same number of atoms per molecule, but different spatial arrangment) is 2,2,4-trimethylpentane:



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Blend in mixtures of the two, they serve as in octane rating of fuels.