Hey Dominik!, Good to see you here!

First, Hi Howard!
Second, there is a very informative thread in another composite forum. Double bag is only for process stability and nothing more. The reason for double bagging is to creat during and after infusion a pressure gradient towads the chamber between bag one and two. That way it is made sure that no air goes into the infused part. If there is a leak in bag one as soon as the resin gets there in infusion the resin goes inte the space/vacuum between the two bags instead of air in the infused part.

Hi,
there is no way how a vacuum betweeen two plasic sheets can improve anything but process safety.
Just imagine what happens, when there is no inner vacuum but only the outer vacuum between the two bags. You have no pressure applied from atmosphere, no compaction - nothing.

In wind industry we are talking about infusions with tons of materials - a failed infusion would we very expensive.

BR
Bernd

There's got to be something there besides just safety and redundancy - but I'm not sure what it is.  It keeps coming back around too much for something completely bogus!  I know it is possible to push resin back out of an infusion with an autoclave so it might be doable to use a second bag and a differential vacuum... the intensifiers without wrinkle-risk seem interesting too.

I've never tried double bag with infusion - only ever double bagged pre-preg cook bags for $$ stuff - and then the best part was how well it pushed down the inner line of sealant tape!  Totally buy the process reliability thing for high stakes parts.

Has anybody here actually tried the method described in the article?

Yes, as well as making large tools such for wind blade tooling (I was previously R&D/Process manager for Gurit Tooling). Double bagging is important to lower the risk of a failed infusion. The cost to double bag vs losing a full blade or mould justifies this.

Hi,
in Wind Industry  rotorblade production this is quite common as well.

BR
Bernd

Exactly ^

I'm yet to believe this is anything more than 'snake oil'. Totally understand it increases vacuum integrity, and so I can see why companies like Boeing use it because as Hojo said it reduces risk. But to suggest people are getting fibre fractions of 70% simply because of double bagging - I don't believe it. It seems like a good marketing strategy and not much more.

https://www.compositesworld.com/articles/double-bag-infusion-70-fiber-volume