Here's something I've been looking at on the back burner for a while. It all started whilst looking for the helmet chin cup which I understand is attribited to Lee Malone and generally thought to be from a UK Police riot helmet. For those that haven't held one they're made of a soft plastic not unlike milk is now sold in, HDPE or similar and very flexible.
Considering this and the fact that the prop makes appears to have doctored the items they used as little as possible it seemed feasible that the chincup and straps came from the same source as the interior helmet cradle. Problem is that if the Boba helmets were constructed in the 70s that the police in this country didn't really use that kind of equipment then. If you look at pictures of the 1981 Brixton riots there isn't much riot equipment on show. In fact Nato helmets (as is the usual term for a riot helmet in the UK Police forces) weren't widely in use until the mid 80s. Secondly, the interior cradle of Nato helmets is generally close, thick padding like modern motorcylce helmets and there is no suspended cradle. The suspended cradle in the Boba helmets has more in common with the interior of a standard 'Custodian' Helmet (Policeman's top hat). However the Boba interior cradle has adjustable sizing and all Nato and Custodian Helmets are sized for the wearer and are not adjustable. As a sidenote here let me say that if you're looking for one of those chincups then you'll have better luck looking for a post 1960s but pre 1990s custodian helmet than an Early Nato helmet. Those models generally feature the chin cup but the wearer usually chooses to tuck the chin strap and cup in the inside of the hat.
Then I looked at my old caving and mountaineering helmet which bears a remarkable resemblance to the interior cradle of the Fett helmet but isn't an exact match. To cut through further waffle I have narrowed the list down to three early models:
The Joe Brown (or JB) climbing Helmet.
The Ultimate Climbers helmet &
the Compton Climbing Helmet Mk ii (which incidentally features the exact same chincup as is used on the Boba Helmets) and possibly the MK i.
Other possiblities will include motorcycle helmets which share much in common with the early climbing helmets and builders hardhats from the period although I've not found anything that close in motorcycle and builders hats yet.
Here is a picture of the closest match I have yet found. Ignoring the colour differences it really is very close.
I haven't yet managed to tally up a model that features the correct chin straps, cup and cradle but it might be out there however it could also be that the cradle and the chinstrap and cup are from different sources; these things are all incredibly hard to come by and I'm now at the stage of making donations to museums and collections in the quest for better images to further the research...
Live the dream