The temporary permit of stay (in italian "permesso di soggiorno provvisorio") is issued by the Immigration Office at Questura. Foreigners can apply to this type of permit to travel and stay in the Schengen area while waiting for the permit of stay. So when they don't hold a permit (but only the postal receipt) and when their entry visa is expired or is valid only for Italy. 

The documentation required is:

• 1 passport size photo
• Passport
• Proof of the travel (invitation letter or registration to a conference or other documentation to show the reason of the travel)
• Copy of the document concerning the appointment at Questura
• The postal receipt 
• A stamp of €16

The temporary permit (permesso provvisorio) has to be requested some days/ a week before the departure and it is issued for work reasons, health reasons and other “important” reasons (so not for tourism purposes).

It is valid only for the period foreigner needs to travel.

Opening hours at Questura of Trieste to request the temporary permit of stay: Mondays and Thursdays from 2:30 to 5:00 pm.