Insulating Materials, Properties, and Selection
Chapter Introduction
This chapter is the core of the insulation trade (thermal and refrigeration). Before installing a single metre of mineral wool or cutting a section of pipe covering, you must master the physical properties of insulating materials, their classification according to Canadian codes and standards, and the selection criteria that guide every application. The Red Seal exam doesn't test your ability to memorize technical data sheets; it evaluates your professional judgment in real-world scenarios. This chapter gives you the tools for that judgment.
2.1 Fundamental Definitions and Units
2.1.1 Thermal Conductivity (k or λ)
Thermal conductivity (k) measures a material's ability to conduct heat. It is expressed in W/(m·K) (watts per metre-kelvin). The lower the k value, the better the insulator.
Typical values: mineral wool k ≈ 0.035–0.045 W/(m·K); polyurethane k ≈ 0.022–0.028 W/(m·K); cellular glass k ≈ 0.045–0.055 W/(m·K).
Factors influencing k: mean temperature (k increases with temperature), density, moisture (water has k ≈ 0.6 W/(m·K), about 15 times that of air), and aging (for gas-blown foams).
> Exam Trap: You're given a k value at 24 °C and another at 150 °C. Never compare them directly. The ASTM C177 or C518 standard requires specifying the mean temperature. The k increases by approximately 10–15% between 20 °C and 200 °C for most wools.
2.1.2 Thermal Resistance (R)
Thermal resistance (R) is the inverse of thermal conductance. For a given thickness (e in metres), R = e / k. The unit is m²·K/W.
Total R of a multi-layer system: R_total = R₁ + R₂ + R₃ + ... (arithmetic sum).
Surface R: internal and external surface resistances (Rsi, Rse) are also added. For a vertical wall, Rsi ≈ 0.12 m²·K/W and Rse ≈ 0.03 m²·K/W (depending on wind speed).
2.1.3 Thermal Transmittance Coefficient (U)
The U coefficient (or U-value) is the inverse of total resistance: U = 1 / R_total. It is expressed in W/(m²·K). The lower the U, the better the building envelope.
Calculation Example: A wall has a total R of 3.5 m²·K/W. U = 1 / 3.5 = 0.286 W/(m²·K). If the temperature difference is 40 °C and the surface area is 20 m², the heat flow is Q = U × A × ΔT = 0.286 × 20 × 40 = 228.8 W.
2.1.4 Water Vapour Diffusion Resistance (µ) and Permeance
The water vapour diffusion resistance factor (µ, mu) is a dimensionless number that compares a material's permeability to that of air (µ_air = 1). The higher the µ, the more the material blocks water vapour.
| Material | µ (approx.) | Classification |
|---|
| Aluminum foil (0.02 mm) | > 100,000 | Vapour barrier |
| Polyethylene (6 mil) | 10,000 – 50,000 | Vapour barrier |
| Kraft paper | 100 – 1,000 | Semi-permeable |
| Mineral wool | 1 – 2 | Permeable |
| Cellular glass | 10,000 – 100,000 | Vapour barrier |
Permeance (in ng/(Pa·s·m²)) is the practical inverse of µ. A material is considered a vapour barrier if its permeance is less than 60 ng/(Pa·s·m²) (according to the National Building Code – NBC).
2.2 Classification of Insulating Materials
2.2.1 Fibrous Insulation
Mineral wool (rock wool and slag wool):
Temperature range: up to 650 °C (rock) and 800 °C (slag) for high-density products.
Density: 24 to 200 kg/m³.
Advantages: non-combustible (Class A), resists moisture (does not absorb by capillary action), good acoustic absorption.
Disadvantages: skin and respiratory irritant (PPE mandatory), k slightly higher than foams.
Glass wool:
Temperature range: up to 230 °C (organic binder) or 450 °C (unbonded).
Density: 10 to 100 kg/m³.
Advantages: lightweight, flexible, excellent for ducts and confined spaces.
Disadvantages: settles under load, loses properties when wet (binder degrades).
Ceramic fibre (kaowool):
Temperature range: up to 1,260 °C (standard grade) and 1,430 °C (high-purity grade).
Use: furnace linings, high-temperature gaskets, insulation of hot piping (> 600 °C).
Caution: classified as a potential carcinogen (IARC Group 2B). Respiratory protection mandatory during handling.
2.2.2 Cellular Insulation (Foams)
Expanded polystyrene (EPS):
k: 0.030–0.038 W/(m·K) at 10 °C.
Density: 15 to 40 kg/m³.
Use: foundation insulation, roofing, under slabs. Not suitable for temperatures > 75 °C.
Water resistance: good, but absorbs water by capillary action if immersed (use EPS Type II or III).
Extruded polystyrene (XPS):
k: 0.026–0.034 W/(m·K).
Density: 25 to 45 kg/m³.
Major advantage: closed-cell structure, near-zero water absorption, high compressive strength (250–400 kPa).
Use: perimeter insulation, inverted roofs, cold storage rooms.
Polyurethane (PUR) and polyisocyanurate (PIR):
Initial k: 0.022–0.028 W/(m·K) (HCFC/HFC blowing agent).
Aging: k increases by 10–20% over 5 years (gas diffusion). Manufacturers provide an aged k value (5 years) for R calculations.
PIR: better thermal stability (up to 120 °C) and better fire resistance than PUR (higher limiting oxygen index).
Use: sandwich panels, roof insulation, cryogenic piping (with cladding).
Cellular glass (Foamglas):
k: 0.040–0.055 W/(m·K).
Density: 100–160 kg/m³.
Unique properties: 100% vapour-tight, non-combustible, high compressive strength (700 kPa), usable from -260 °C to +430 °C.
Use: cryogenic tanks, terrace roofs, under-slab insulation on contaminated soil.
2.2.3 Reflective and Vacuum Insulation
Radiant barriers (multi-layer foil):
Principle: reduces heat transfer by radiation (emissivity ε < 0.05 for polished aluminum).
Effective R: depends heavily on orientation and adjacent air space. Never assign a fixed R without standardized testing (ASTM C1373).
Use: ventilated attics, agricultural buildings, high-temperature piping (with spacing).
Vacuum insulated panels (VIP):
k: 0.004–0.008 W/(m·K) (10 times better than wool).
Fragility: any puncture of the metal envelope destroys the insulation (k returns to that of air).
Use: medical equipment, refrigerated transport, high-performance buildings.
2.3 Selection Criteria by Application
2.3.1 Service Temperature
Each material has a maximum continuous use temperature (MCUT) and sometimes a minimum temperature (for cryogenic applications).
| Material | MCUT (°C) | TMIN (°C) |
|---|
| Glass wool (with binder) | 230 | -50 |
| Rock wool | 650 | -50 |
| Ceramic fibre | 1,260 | -100 |
| EPS | 75 | -150 (brittle) |
| XPS | 75 | -100 |
| PUR/PIR | 100–120 | -180 |
| Cellular glass | 430 | -260 |
| Calcium silicate | 1,000 | -50 |
> Golden Rule: If the surface temperature exceeds 60 °C, the insulation must be protected by a finishing covering (metal jacketing, cementitious coating) to prevent burns and limit fire spread. The Canadian Electrical Code, Part I (CE Code) requires a minimum clearance of 25 mm between combustible insulation and an unshielded electrical conductor (Rule 8-200).
2.3.2 Moisture and Freeze Resistance
Moisture is the #1 enemy of insulation. A 1% increase in moisture content by volume in mineral wool can reduce its R by 10 to 30%.
Below-zero applications (industrial refrigeration): insulation must be vapour-tight on the warm side. The vapour barrier must be continuous, without punctures, and joints must be sealed with a compatible mastic.
Freeze/thaw: open-cell materials (wool) absorb water and degrade. Use XPS, cellular glass, or closed-cell polyurethane foam.
Condensation: calculate the dew point. If the exterior surface temperature of the insulation is below the dew point of the ambient air, condensation will occur. Insulation thickness must be increased, or a vapour barrier added.
2.3.3 Fire Resistance and Flame Spread Ratings
The National Building Code of Canada (NBC) classifies materials according to:
RSI (R-value per unit thickness): does not apply to insulation alone, but to the entire wall assembly.
Flame Spread Rating (FSR): measured according to CAN/ULC-S102. An FSR ≤ 25 and a smoke development rating ≤ 50 are required for interior walls and ceilings.
Classification: A (non-combustible), B (combustible with low flame spread), C (combustible).
Specific requirements:
Ventilation ducts: insulation must be non-combustible (mineral wool or cellular glass) if the duct penetrates a floor or fire separation.
Piping penetrating fire separations: insulation must be protected by intumescent caulking or a certified fire stop (ULC S101).
Cold storage rooms: sandwich panels must have a PIR/PUR core with metal facing on both sides (FSR ≤ 25).
2.3.4 Mechanical Strength and Compression
For roofs, slabs, and applications under load, compressive strength (in kPa) is critical.
| Material | Compressive Strength (kPa) | Typical Use |
|---|
| EPS Type I | 35–70 | Walls, non-traffic roofs |
| EPS Type II | 70–105 | Roofs with gravel |
| XPS | 250–400 | Inverted roofs, slabs |
| PIR (board) | 150–250 | Roofs with membrane |
| Cellular glass | 700–1,000 | Roofs with heavy loads |
Thickness Rule: For the same R-value, a denser material has better compressive strength but a slightly higher k. Never sacrifice mechanical strength for a marginal R gain.
2.4 Practical Calculations for the Exam
2.4.1 Calculating Required Thickness
To achieve a target thermal resistance R_target:
e (m) = R_target × k
Example: You need to insulate a steam pipe to achieve R = 1.5 m²·K/W with rock wool (k = 0.040 W/(m·K)).
e = 1.5 × 0.040 = 0.060 m = 60 mm.
2.4.2 Calculating Linear Heat Loss (Piping)
For a pipe with outer diameter D (in m), with insulation thickness e, the heat loss per linear metre is:
Q/L = (2 × π × ΔT) / [ln((D + 2e) / D) / k]
Example: Pipe D = 0.1 m, e = 0.05 m, k = 0.04 W/(m·K), ΔT = 100 °C.
Ratio (D + 2e)/D = (0.1 + 0.1)/0.1 = 2.0
ln(2.0) = 0.693
Q/L = (2 × 3.1416 × 100) / (0.693 / 0.04) = 628.3 / 17.33 = 36.3 W/m
2.4.3 Calculating Dew Point and Condensation
The dew point (Td) is calculated from relative humidity (RH) and dry-bulb temperature (T):
Td ≈ T - (100 - RH) / 5 (approximate formula, valid for RH > 50%)
Example: Air at 25 °C, RH = 70%. Td ≈ 25 - (30/5) = 25 - 6 = 19 °C. If the exterior surface of the insulation is at 15 °C, condensation will occur. You must increase the thickness or add a vapour barrier.
2.5 Applicable Canadian Codes and Standards
2.5.1 National Building Code (NBC)
Section 9.25: Thermal insulation and water vapour control.
9.25.2.2: Minimum R-value requirement for walls (R-19 to R-24 depending on climate zone).
9.25.4.2: The vapour barrier must be installed on the warm side of the insulation, with a permeance ≤ 60 ng/(Pa·s·m²).
9.25.5.1: Insulating materials must be protected against moisture and mechanical damage.
2.5.2 Canadian Electrical Code, Part I (CE Code)
Rule 8-200: Clearance between conductors and combustible insulating materials. A 25 mm clearance is required for unshielded conductors. If the insulation is non-combustible (mineral wool), no clearance is required.
Rule 8-202: Combustible insulating materials must not be in contact with recessed luminaires or transformers (surface temperature > 90 °C).
2.5.3 CSA B149.1 (Natural Gas and Propane Code)
Article 6.14: Gas piping must not be insulated with materials that promote corrosion (e.g., mineral wool containing chlorides). Use neutral-pH materials or cathodic protection.
Article 6.15: Chimney vents must be insulated with non-combustible materials (ceramic wool or cellular glass) if the distance to combustible materials is less than 450 mm.
2.5.4 Material Performance Standards
| Standard | Subject |
|---|
| CAN/ULC-S701 | EPS (Types I, II, III, IV) |
| CAN/ULC-S702 | Mineral wool (rock and slag wool) |
| CAN/ULC-S703 | Glass wool |
| CAN/ULC-S704 | Polyurethane and polyisocyanurate boards |
| ASTM C177 | Thermal conductivity (guarded hot plate) |
| ASTM C518 | Thermal conductivity (heat flow meter) |
| ASTM E96 | Water vapour permeance |
2.6 Installation Procedures and Best Practices
2.6.1 Surface Preparation
Before installing any insulation:
130.Clean the surface (oil, rust, dust) to ensure adhesion of adhesives and coverings.
131.Check the condition of the piping or equipment (corrosion, leaks). Never insulate an active leak.
132.Apply an anti-corrosion primer on hot metal surfaces (temperature > 60 °C) before installing insulation.
2.6.2 Installing Pipe Sections and Boards
Pipe sections: install in a staggered pattern (offset joints) to avoid thermal bridges. Secure with bands or temperature-resistant tape.
Boards: fasten with welded studs or compatible adhesives. Joints must be flush and filled with mastic if vapour-tightness is required.
Double layer: if the total thickness exceeds 75 mm, install in two layers with offset joints. The inner layer must be tight; the outer layer can be slightly looser.
2.6.3 Vapour Barrier and Covering
Warm side: the vapour barrier (aluminum foil, polyethylene) must be continuous and sealed at all joints (tape, mastic). Punctures (supports, probes) must be sealed immediately.
Cold side: a permeable covering (perforated metal, mesh) allows residual moisture to escape.
Finishing covering: aluminum jacketing (0.5 mm min.) for impact-prone areas, cementitious coating for wet areas, intumescent paint for fire-rated areas.
2.7 Pitfalls to Avoid
143.Confusing k and R: k is a material property (constant), R depends on thickness. R = e/k. A material with a low k isn't necessarily better if the thickness is insufficient.
144.Using the k value at 24 °C for a 300 °C application: always correct k based on the mean service temperature.
145.Forgetting foam aging: the k of PUR/PIR increases over time. Use the aged value (5 years) for design calculations.
146.Neglecting the vapour barrier on the warm side: in cold Canadian climates, vapour migrates from inside to outside. A poorly installed vapour barrier causes condensation and loss of R.
147.Insulating electrical equipment without checking the CE Code: Rule 8-200 requires a 25 mm clearance for unshielded conductors. Combustible insulation in direct contact is a violation.
148.Using mineral wool on gas piping: chlorides in certain binders cause pitting corrosion (CSA B149.1, Article 6.14).
149.Calculating pipe heat loss with the flat wall formula: for pipes, you must use the logarithmic (cylindrical) formula. The error can reach 30% for small diameters.
150.Forgetting surface resistances: in calculating the U of a wall, Rsi and Rse must be included. Ignoring them overestimates thermal performance.
151.Choosing insulation based solely on price: total cost (material + labour + maintenance + lost energy) must be considered. A cheaper insulation with a higher k can cost more over 20 years.
152.Not checking chemical compatibility: certain adhesives and mastics dissolve EPS. Use products without aggressive solvents (e.g., acrylic mastic, not neoprene glue).
2.8 Tips for the Red Seal Exam
Memorize temperature ranges: MCUT for each material. This is a classic multiple-choice question.
Master conversions: 1 W/(m·K) = 0.578 Btu/(h·ft·°F). 1 m²·K/W = 5.678 h·ft²·°F/Btu. Questions may mix units.
Learn formulas by heart: R = e/k, U = 1/R_total, Q = U × A × ΔT, Q/L (cylindrical). You won't have a formula sheet on the exam.
Know standards by their full names: "Canadian Electrical Code, Part I" and "CSA B149.1". Questions reference rule numbers (8-200, 6.14).
Visualize scenarios: you're given a situation (e.g., insulating a cold storage room at -25 °C). Immediately identify the appropriate material (XPS or PIR with vapour barrier) and the risks (condensation, freezing).
Practice condensation calculations: dew point is a recurring question. Practice with typical values (20 °C, 50% RH → Td ≈ 10 °C).
Summary
Thermal conductivity (k) is the intrinsic property of a material; resistance (R) depends on thickness. R = e/k.
Fibrous materials (rock wool, glass, ceramic) are non-combustible and heat-resistant, but absorb moisture.
Foams (EPS, XPS, PUR/PIR) offer lower k but are combustible and sensitive to high temperatures.
Cellular glass is the only vapour-tight and non-combustible material, suitable for extreme temperatures (-260 °C to +430 °C).
Selection depends on: service temperature, moisture, fire resistance, compression, and chemical compatibility.
The vapour barrier must always be on the warm side, with a permeance ≤ 60 ng/(Pa·s·m²) (NBC 9.25.4.2).
CE Code, Rule 8-200 requires a 25 mm clearance between combustible insulation and unshielded electrical conductors.
CSA B149.1, Article 6.14 prohibits insulation containing chlorides on gas piping.
Heat loss calculations for piping use the logarithmic formula, not the flat wall formula.
Foam aging increases k by 10–20%; always use the aged value for design.
Pitfalls to Avoid (Reminder)
| Pitfall | Consequence | Solution |
|---|
| Confusing k and R | Incorrect thickness calculation | R = e/k, always |
| Ignoring mean temperature | Under-sizing | Correct k based on MCUT |
| Forgetting aging | Actual performance lower | Use aged k (5 years) |
| Vapour barrier misplaced | Condensation, mould | Warm side, continuous, sealed |
| Insufficient electrical clearance | CE Code violation, fire risk | 25 mm min. (Rule 8-200) |
| Mineral wool on gas piping | Corrosion (chlorides) | Neutral-pH material (CSA B149.1) |
| Flat wall formula for pipes | 30% error | Logarithmic formula |
| Forgetting Rsi/Rse | Overestimated U | Include surface resistances |
| Chemical incompatibility | Insulation dissolution | Check adhesives/mastics |
| Choosing by price alone | Higher total cost | Life cycle analysis |
This chapter covers all the concepts required by the Red Seal for the "Insulating Materials, Properties, and Selection" block. Review the temperature tables and formulas before moving on to the following chapters.
