The following insulation table was compiled from various sources in the references below. The selection is intended to be of use to solar/renewable energy DIYers. See the manufacturer for actual values for specific products.

If you're not familiar with insulation at all or what R-value means then have a look at the insulation page first.

Sample photos of different types of insulation

It's not recommended that polystyrene be used for most solar heating applications due to it's low melting temperature. If you want to use a rigid board then most often polyisocyanurate is used.

Polyisocyanurate rigid board (foil faced).
Polyisocyanurate rigid board (foil faced), Source: thingermejig.
Extruded polystyrene rigid board in window solar air heater.
Extruded polystyrene rigid board in window solar air heater.
Extruded polystyrene rigid board in window solar air heater.
Extruded polystyrene rigid board in window solar air heater.

A batt is a blanket or roll of insulation.

Mineral/rock wool batting.
Mineral/rock wool batting, Source: Achim Hering.

Table of insulation commonly used in DIY solar/renewable energy projects

Material R-value
per inch (US)
R-value
per thickness
Working
temperature
Notes
polyisocyanurate rigid board (foil faced) 6.8 - 7.7   200F (93C)  
polyurethane rigid board (foil faced) 6.8   200F (93C)  
extruded polystyrene rigid board 5.0   165F (74C)
expanded polystyrene rigid board 3.6-4.4   165F (74C) Combustable. Not a good choice for a solar collector. This is the white one. Also in the form of "peanuts".
fiber glass batts 3.0 - 4.3   180F (82C) Good fire resistance.
mineral/rock wool batts 3.0 - 4.0   > 500F (> 260C) Excellent fire resistance.
straw bale 1.45      
wood (general) 0.75 - 1.41      
wood (oak) 0.75      
wood (pine) 0.91 - 1.32      
wood (cedar) 1.09 - 1.41      
plywood 1.25      
glass - single pane   0.91    
glass with 1/4" air gap   1.69    
glass with 1/2" air gap   2.04    
glass with 3/4" air gap   2.38    
low-E glass (0.20) with 1/2" air gap   3.13    
Suntuf polycarbonate sheet (Palram)   0.68    
6mm Twin Wall polycarbonate sheet (Macrolux)   1.58    
8mm Twin Wall polycarbonate sheet (Macrolux)   1.72    
10mm Twin Wall polycarbonate sheet 1700 g/m2 (Macrolux)   1.77    
10mm Twin Wall polycarbonate sheet 2000 g/m2 (Macrolux)   1.89    

References:
1. Choosing your Wood Species. LogHome.com
2. Thermal conductivity. Wikipedia
3. R-value (insulation). Wikipedia
4. Insulation Factsheet. University of Alaska Fairbanks - via builditsolar.com
5. R-Values Table. COLORADOENERGY.org
6. Suntuf Physical Properties Sheet. palramamericas.com
7. Long Life twin and triple wall polycarbonate sheets (Macrolux). macrolux.co.uk

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