( ( Materials ( which ( ( do not ) ( ( allow ( an ( electric current ) ) ) ( to ( flow well ) ) ) ) ) ) ( ( are ( called insulators ) ) . ) )
(ROOT (S (NP (NP (NNS Materials)) (SBAR (WHNP (WDT which)) (S (VP (VBP do) (RB not) (VP (VB allow) (NP (DT an) (JJ electric) (NN current)) (S (VP (TO to) (VP (VB flow) (ADVP (RB well)))))))))) (VP (VBP are) (VP (VBN called) (NP (NNS insulators)))) (. .)))
Materials which do not allow an electric current to flow well are called insulators.
(ROOT (S (NP (PRP You)) (VP (VBP call) (NP (NP (NNS materials)) (SBAR (WHNP (WDT that)) (S (VP (VBP have) (NP (JJ high) (NN resistance)) (PP (TO to) (NP (JJ electric) (JJ current) (JJ electric) (NNS insulators)))))))) (. .)))