[time-nuts] Thermal insulation choice?

[Jim Lux]

On 1/6/12 11:39 AM, John Ackermann N8UR wrote:
> I am looking for a readily available (from Home Depot or other local
> source) insulating material to use in a chassis that's housing a
> sensitive OCXO. My goal is just to slow down any external thermal
> transients so the oven loop has time to react gracefully.
>
> I'm thinking of something in sheet form that I could glue to the inside
> bottom and side of the metal chassis. The trimmed sheet sizes will each
> probably end up being around 4 x 8 inches. I have enough clearance for a
> thickness of a half inch or so. I'd like to avoid a bat material as that
> would be hard to mount neatly.
>
> Long lifetime (ie, not getting all crumbly after a few years) is
> important as I don't expect this oscillator to get cold until I do.
>
> Any suggestions of a material to look for?
>

There are a variety of foams available. Expanded Polystyrene (EPS) foam 
(styrofoam) is one,and readily available, but typically fairly low 
density (sort of like big cottage cheese blobs). Also called "beadboard" 
(which name is obvious if you've seen degraded styrofoam icechests). 
It's got tiny passages which let water migrate through, so in commercial 
insulation, you need impermeable face sheets.

Extruded Polystyrene foam (aka XPS or XEPS) is blue or pink board.  It's 
what's used in construction a lot. It's a higher density (in a kg/liter 
sense) than EPS with more uniform smaller bubbles.  Easily sawed, 
sanded, etc. (an electric carving knife works great).

Polyisocyanurate and Polyurethane.  Polyisocyanurate is the stuff with a 
foil backing layer.

For the same thickness, the latter foams have a higher R-value (maybe 
50% higher).


Lowes has insulfoam R-tech 1"x2'x4' for $3 according to the web (with 
poly, not foil, face sheets) .  That's a expanded polystyrene.