Aldi Special on superfoil SF6

[Radian]

 Aldi are currently slinging "airtight multilayer foil insulation designed by SuperFOIL with the DIY customer in mind"

 

 

According to the SF6 data sheet its Water Vapour Resistance is 1200MNs/g which makes it vapour tight in addition to being airtight.

I understood that this was a no-no in the kind of application they're pushing here?  WIth an R-value of just 1.9 that's going to be a cold surface for vapour to condense on.

Am I missing something?

[SteamyTea]

Isn't this just bubble wrap with tin foil on it.

[Radian]

1 minute ago, SteamyTea said:

Isn't this just bubble wrap with tin foil on it.

 

No, 6 layers of something 

[MikeSharp01]

Perhaps 2 layers of tin foil and 4 layers of bubble wrap then When I used this many years ago it had multiple foil layers separated by what looked like fleece (thinsulate)

[epsilonGreedy]

4 hours ago, Radian said:

According to the SF6 data sheet its Water Vapour Resistance is 1200MNs/g which makes it vapour tight in addition to being airtight.

 

 

I thought we all tried to avoid such vapour tight products in the loft?

[Radian]

11 hours ago, epsilonGreedy said:

 

I thought we all tried to avoid such vapour tight products in the loft?

 

Yes, this is an area I'm currently looking at making improvements in. My understanding is that a ventilated loft such as mine should retain an open path for water vapour coming up from the house to be naturally extracted with the regular air changes in the loft. I would hazard a guess that the majority of the UK housing stock is like this, certainly in houses built pre 21st century.

 

I'm quite sure these non-breathable products aren't aimed at the EnerPHit or passive house markets but they are certainly the cheapest forms of insulation on sale. This will have plenty of people, unaware of the issues, installing it and creating problems with rot and water damage. I think this would be irresponsible.

 

However, this product caught my eye because I'm considering investing £630 for 6 rolls of YBS BreatherQuilt 2 in 1 Multi Layer Insulation Blanket which has a very low vapour resistance (0.15MNs/g) to drape over the top of 300mm rockwool to give me a maintainable surface and boost the total R-value a little. Just a little...

 

...I really only want the perforated foil layer as the r-value of this blanket is 1.6 whereas the 300mm rockwool underneath should be around 6. And I suspect that when laid flat the blanket drops to more like 1.

 

However, I'm not having much luck finding just a reflective breather membrane that is significantly cheaper than this blanket. I guess I could just use Tyvek but I'd rather it was shiny because "shiny is practically the same thing as useful"

[Radian]

I just found one more properly breathable blanket style product Superfoil SF19BB This one has a few more layers giving a reported R-Value of 2.2 so roughly equivalent to one 100mm layer of rockwool. It's a bit more expensive than the YBS but more insulating and a tiny bit more breathable at 0.115MNs/g

 

Annoyingly I also found exactly what I want - if only it really were breathable:

 

 

"Vapour Barrier & Waterproof breathable Membrane" must mean air breathable? After all, if it's a vapour barrier then what's it breathing? Air sans water vapour? I guess that might be possible but from the look of it nothing's going to get through. I just love the customer Q&A on this very point:

 

 

Very helpful ?

Edited January 11, 2022 by Radian

[Radian]

Turns out superfoil also have a single-ply breather membrane (like Tyvek) called SFBB but it's not shiny ?

Apart from that I guess it's exactly what I wanted. But not sure how 'maintainable' the surface would be.