Xps board vs polystyrene sheets

[Moth]

The majority of my grow is now yellowing and have an idea of the required kiln volume.

Anyhow - the Kiln insulation of choice appears to be XPS (Extruded Polystyrene) boards.

There's a significant price difference compared to plain polystyrene insulation boards, which are 3 times cheaper.

Polystyrene:

• Coverage: 2.88 m²
• Thermal Conductivity: 0.038 W/mK
• Thermal Resistance R Value: 1.32 m2K/W
• Usage: Insulation

XPS

• Coverage: 2.88 m2
• Thermal Conductivity: 0.022 W/mK
• Thermal Resistance R Value: 1.80 m2K/W
• Type: Insulation Boards

OK, so the XPS is 0.018 W/mK less thermally conductive, and has an R Value delta of 0.48 m2K/W compared to polystyrene. I understand a higher R value is better, although, in real terms - the figures are meaningless to me.

These values could mean they are both excellent insulation and I won't notice, or, could mean polystyrene is awful and will leak heat like an open door. No idea what's a good range of R values.

Also having a hard time reconciling the quoted figures with the data here https://en.m.wikipedia.org/wiki/R-value_(insulation)

So, given the price difference (and we'll ignore working with polystyrene is trickier than XPS), does anyone think polystyrene is going to perform well/well enough that I don't regret it?

I mean, I could use twice as much compared to XPS (double skin the polystyrene), get a far better R value than XPS and still only cost 66%...

Anyone else use polystyrene?

I had a minor concern about off gassing, although, plan to use a ChinaVoodoo method variant (brewing buckets . mason jars etc) within the kiln

Thank you for any thoughts

 

[ChinaVoodoo]

Fyi, Mason jars with steel lids will likely rust shut.

I think either foam will work. I used the polystyrene with the foil coating. It acts as a barrier, and it improves efficiency above that which is implicated by r value.

 

[deluxestogie]

use twice as much compared to XPS (double skin the polystyrene), get a far better R value than XPS and still only cost 66%

I believe that is a good idea thermally. (My 2" XPS is not quite efficient enough. I can, unfortunately, use my kiln to add some heat to a seedling tray rested on top.) Another aspect of the discussion is whether or not you will be relying on the foam sheeting to add structural integrity. The XPS is not too bad on its own (with no wood frame--just taped with Tyvek tape), though I did not use it in that manner for my kiln.

Likely the most important aspect of thermal efficiency is the seal on the door or closure. If water vapor wafts away, then substantial amounts of heat are lost. If you go with a dry Crockpot and closed jars, then it may not be as important.

For lids on jars at under 130°F, I believe (though I've not tested it) that plastic Mason jar lids will do fine. Standard size lids are the very same as those on (American) mayo jars. Wide-mouth plastic lids are available now at a fairly low price. They won't hold up to boiling+ temps, but kiln temp is way below that.

Bob

 

[Jitterbugdude]

You do not need the rings on the mason jars when you are kilning. If you feel the need, you can put them on very loosely. I vent mine once per day (usually with the rings on) and have never come close to having them rust.

 

[ChinaVoodoo]

I had to break a couple jars to get the tobacco out.