Hoods

[Deep6]

I am actually curious about a wide range of issues surroundning the choice of hoods in cold water diving, but to begin with I am curious about nitrogen-blown neoprene. In technical terms, what are the specific advantages of pure nitrogen in neoprene?

[Richard Lundgren]

I am actually curious about a wide range of issues surroundning the choice of hoods in cold water diving, but to begin with I am curious about nitrogen-blown neoprene. In technical terms, what are the specific advantages of pure nitrogen in neoprene?

The major benefit would be that a nitrogen hood keeps it shape better compared to a conventional hood material. A normal 5 mm hood becomes thin as a lief only after a few deep dives.

[Deep6]

A nitrogen hood keeps its shape better compared to a conventional hood material.
Yeah, I've heard this, but never understood why. Is it the gas qualities of pure nitrogen that causes this? More 'bounce' after compression? Or is it due to the lack of oxygen somehow?

[Richard Lundgren]

Yeah, I've heard this, but never understood why. Is it the gas qualities of pure nitrogen that causes this? More 'bounce' after compression? Or is it due to the lack of oxygen somehow?

As if understanding decompression and the effect of hydrogen-peroxide in relation to oxygen seizures wasn't enough, now I need to figure our why nitrogen in neoprene bounces around too :) . Sorry mate, I have no idea.

[Deep6]

Well, imagine how I felt, dumbfounded without an answer standing in front of a PADI Open Water class... :)

I got out of it, as usual, by simply stating "Dude, the shit rocks" - but it sparked yet a personal quest for answers! ;)

Thank goodness for internet, however; as this site gave me a little more info: http://www.wetwear.com/rubatex_g-231n.htm

Particularly, I noticed "The thicker the cell wall the more pressure the cell can withstand without losing nitrogen gas". However, this tells me that the quality of the neoprene lies in witholding gas in the cells during compression (thicker cell walls), but doesn't tell me why pure nitrogen is better than air. Perhaps it is because N2 is a larger molecyle tha O2?

[Eirik Kjos]

I might be wrong, but my understanding is that a chemically blown neoprene genrally has fewer but bigger bubbles in the material, thus making it more prone to compression at depth, and ultimatly chrushing (where the walls between the bubbles collapse), leaving it more or less useless after a few dives. However the neopren that has been made with more, but generally smaller bubbles is what you want, as the chrushing is less of an issue.

If you make neopren by adding nitrogen to the rubber material under extreme pressure, high quality neopren is a result, with small but very consistent bubbles, and thus not prone to chrushing, nor as prone to compression as the neopren wall is thicker.

So the resulting neoprene is what your looking for, not the nitrogen in it self.

Eirik K

[Deep6]

That is at least consistent with the article, so it sounds like a good answer to me! :) In summary:

The nitrogen facilities the creation of more evenly spread bubbles with thicker cell walls, which is the result that makes the nitrogen-blown neoprene a higher quality than chemically-blown neoprene.

In terms of evaluation a good hood for cold water diving, what else may be considered, then? Shape, stitching? :confused: I find I've never been happy with a hood's fit around my neck...

[Richard Lundgren]

That is at least consistent with the article, so it sounds like a good answer to me! :) In summary:

The nitrogen facilities the creation of more evenly spread bubbles with thicker cell walls, which is the result that makes the nitrogen-blown neoprene a higher quality than chemically-blown neoprene.

In terms of evaluation a good hood for cold water diving, what else may be considered, then? Shape, stitching? :confused: I find I've never been happy with a hood's fit around my neck...

smaller, more and evenly spread bubbles :p

[Deep6]

smaller, more and evenly spread bubbles :p
Didn't you just say you didn't know, bro?! In that case "shhh"... because nobody likes a smartass! ;)

Just clownin' :D One love!

[Richard Lundgren]

Didn't you just say you didn't know, bro?! Then "shhh"... because nobody likes a smartass! ;)

I just pretended bro to get the discussion going, promise :D No, seriously Eric was the one that cracked the nut but I liked the idea of small bubbles. Kind of links things back to decompression again. These small bubbles do need our love and attention

[Jan wilske]

I think it is by the same reason they use nitrogen to make industrial whipped cream. The oxygen in air will react with the manufactured stuff (cream or neoprene) when they make it.

best regards

Jan Wilske

[Deep6]

Richard, I am told you have experienced that rubatex material get stiffer in cold weather (subzero temperatures)...

If the nitrogen-blown neoprene is more dense, I guess that would be a relative effect of freezing? The denser the neoprene the more stiff it would get. Did this have any lasting effect once you brought the material under water?