R-Value of Foil Bubble Wrap?

[TomD]

what is the value of foil bubble wrap?. AC installer wants to use it. is it any good? if not what should i use? Duct work is in the attic with fairly long runs, over 40ft. I am in the NY / NJ area.

[Lloyd E. Sponenburgh]

TomD fired this volley in news: [e-mail]:

Bubble-wrap style radiant barrier varies in R value depending upon its use and its environment.

It's specifically designed to block radiant energy in the visible and infrared spectra. At that task, good quality material can be around 97% effective, and can show an "effective R" of up around 19. (It must block

97% to qualify for the name "radiant barrier material")

However, it degrades in performance if exposed to ultraviolet for long. Its polyethylene overcoating becomes cloudy, and begins to absorb radiant heat, rather than reflect it.

It's a poor insulator for the purpose of acting as a barrier between different air temperatures, dropping down to an R-2 value in that service.

LLoyd

[-zero]

Here's a quasi-related study report performed in Canada.

I wouldn't use it as a first choice for anything. YMMV.

-zero

[TomD]

----------Snip----------------------

Then I gather, Foil Bubble Wrap Insulation is not effective for A/C ducts, which are located in the attic. Temp there can be well over 100 degrees. Is this a correct interpellation? What is the best reasonable priced material to use for duct work trunk lines?. I do realize you get what you pay for. Thanks

[Lloyd E. Sponenburgh]

TomD fired this volley in news: [e-mail]:

You didn't describe the ducting. If it's made-up metalwork, you'd _better_ get some insulation on it. Most residential work seems to end up as flex or ductboard, primarily because it requires much less skill to install than metal. Most installers don't have the skills to make custom metal. Typically, they're using pre-fabbed components, and just hooking them up.

Flex duct and ductboard are already insulated to one degree or another. Older stuff was about R-2.5; new material is usually R-6.

You have two primary insulation issues to deal with, and an ancillary one. The first is the air temperature in the attic. That requires thermal insulation -- foam, fiberglass batt, or fiberglass pressed board. The second is radiant (IR) energy booming down from the roof surface. That requires a radiant barrier film. It's best placed on the underside of the attic rafters, but flex duct can have it as the outer barrier layer (Silvaflex, etc). Most ductboard typically has an aluminum radiant barrier outer layer.

The third issue is to provide some sort of vapor barrier between the potentially humid attic space and the cool outer surface of the duct liner. Again, flex and ductboard accommodate this with the outer barrier layer, which, if it's taped and mastic'd properly will keep out moisture. Metalwork must be properly wrapped and sealed to prevent moisture traveling to the cool surface, and condensing there. If the thermal insulation layer gets wet, the R value essentially drops to nada in the wet areas.

Commercial work in our area uses either a wrapped fiberglass batt topped off with a continuous layer of mastic, or a spray-on foam material.

The foam is a superior insulator AND moisture barrier combined, but for commercial installs (here), it must be covered with intumescent paint in order to meet fire codes.

You have a lot of options -- but first it boils down to the original question; What type of ducting do you have?

LLoyd

[Abby Normal]

Its a product that is better suited for keeping heat out than in. Under slab is a poor application for it. Following the underside of a roof deck with an air space is a better application.

[Bob Pietrangelo]

Thje bubble wrap has an insulating factor of R-6 if I remeber correctly. BUT---it has to be installed properly. Most guys just wrap it around the duct. You have to properly install spacers between the duct and the insulation. If you don't it aint worth shit. If they are going to use it watch them, if not make them use an R-8 blanket insulation.

[Bob Pietrangelo]

There are local and national codes that determine your minimum duct insulation in an unconditioned space. There are lots of ways to achieve it.

[Bob Pietrangelo]

17 friggin posts and not one is relevent, lloydy boi is discussing rooftop insulation, when the op stated it was in an attic, everyone else is trying to beat up on one or the other, jeez

[-zero]

Yea, I can see that working. I went back to Google and found a few web sites pimping their version of the product. Like you say, under a roof deck, or stapled across exposed roof rafters, reflecting the radiant of a merciless Florida sunny day. I recall the times I neglected to throw up my foil-like windshield sun visor for the duration of a sunny day... and YES, it works VERY well for that application. I TRY not to let that happen very often, though. :o)

-zero

[Lloyd E. Sponenburgh]

"Bob Pietrangelo" fired this volley in news:FvmdnQYyQJiYMWzbnZ2dnUVZ [e-mail]:

Not, really Bob. ONE issue was radiant barrier on ducting, and where it is best placed -- which is as part of the roof structure, rather than on the ducts themselves.

LLoyd