"due to" or "because of"?

Because of and due to are used to explain a reason. They're followed by a noun or noun phrase.

Schools were closed because of heavy snowfall.
The flight was delayed because of bad weather.
All planes are grounded due to fog.
The delay was due to heavy traffic.
The concert was cancelled due to rain.

Due to or Because of?

Due to modifies nouns. It's used after verb to be (is, are, was, were, etc.)

Jan's success is due to talent and work (due to modifies 'success')

Because of modifies verbs.

Ted resigned because of poor health (because of modifies 'resigned')

My loss of appetite was due to a stomachache (due to modifies 'loss of appetite')
I lost my appetite because of a stomachache (because of modifies the verb 'lost')