Great idea.  I was looking to see if there were any publically available schematics, but have not found any.   Having a port for a straw or tube feeding access will be important.  If the flow rate into the helmet is 45-60 Liters/minute, Co2 buildup won't be an issue.  It will need a HEPA filter at the exhaust, BOSCH makes a car cabin one that is about $17 U.S.  One used for a vacuum cleaner would be okay too since it is on the exhaust end.  From the articles I've read, they are a better option for many clinical situations than a standard CPAP mask.  Avoiding intubation/vent is such a great idea, too much barotrauma on the vent.  

very much want to gather the knowledge and materials to build a batch of these. I have some experience with heat sealing PTFE .05 mm thick into 2.5 m x  1m x 1m bags that had to be airtight.

You mentioned in  item 4 you have a contact at a company building them in Italy. 

Can you get us any help with the following:

*Materials used for the different parts?

**Information about equipment 

***Information about techniques 

Seems like a great idea to build these to free up some ventilators for the sicker patients. 

add covid-19 and coronavirus to title so users can find it

these Noninvasive Ventilation Helmets are out of stock everywhere how can you promote this idea