Introduction
This glossary defines every key term you will encounter when specifying, purchasing, or installing pipe insulation in the UK.
A
Adhesive — Contact adhesive for bonding elastomeric foam joints. Armaflex 520 is standard for Armaflex EVO. Apply to both faces, allow to become tacky, press firmly. See: How to Cut and Install Pipe Insulation.
Aluminium foil facing — Factory-applied foil on phenolic foam (e.g. Kooltherm) acting as vapour barrier (μ > 100,000). Must be kept intact at all joints. See: Vapour Barriers, Foil-Faced vs Elastomeric Foam.
Armaflex EVO — Standard Armacell elastomeric foam. λ = 0.033 W/m·K, μ ≥ 10,000, −200°C to +105°C, Microban protection, Euroclass B-s2,d0. See: Armaflex vs K-Flex.
Armaflex HT Solar — EPDM foam for solar thermal and high-temperature outdoor use. Rated to +150°C, UV-stabilised. See: Outdoor Pipe Insulation.
Armaflex Tuffcoat — Pre-jacketed Armaflex EVO with PVC outer coating for outdoor and underground use. See: Outdoor Pipe Insulation.
B
Bore size — Internal diameter of insulation section, matched to pipe OD. “15mm bore” fits 15mm nominal bore copper pipe (18mm OD). See: What Thickness Do I Need?
BS5422 — Primary UK standard for pipe insulation specification. Provides minimum thickness tables for heat loss and condensation control. Referenced by Part L. See: BS5422 Explained.
Butt joint — End-to-end joint between two insulation lengths. Must be bonded (elastomeric foam) or taped (mineral wool). See: How to Cut and Install.
C
Closed-cell foam — Foam with sealed cells. Resists water vapour and does not absorb liquid water. Armaflex EVO and K-Flex ST are closed-cell. See: Vapour Barriers.
Cold bridging — Localised heat transfer at pipe supports or penetrations causing condensation. Prevented by insulated pipe supports with a thermal break.
Condensation — Water vapour converting to liquid on a surface below the dew point. See: Condensation on Copper Pipes, Vapour Barriers.
Condensation control — Use of closed-cell insulation with vapour barrier to prevent condensation on cold pipes. See: Chilled Water Insulation, Cold Water Insulation.
D
Dew point — Temperature at which water vapour begins to condense. Outer surface of cold pipe insulation must stay above the dew point. See: Vapour Barriers.
DHW — Domestic Hot Water, typically at 60°C. Must be insulated to BS5422 under Part L. See: Domestic Heating.
E
Elastomeric foam — Flexible, closed-cell rubber foam. Standard for cold pipe applications. Key products: Armaflex EVO, K-Flex ST. See: Armaflex vs K-Flex, Foil-Faced vs Elastomeric.
EPDM — Synthetic rubber for high-temperature and UV-resistant insulation. Armaflex HT Solar is EPDM, rated to +150°C.
F
Frost protection — Insulation slows heat loss and delays freezing but does not prevent it indefinitely. See: Outdoor Insulation, Cold Water Insulation.
H
HTHW — High Temperature Hot Water, above 120°C. Requires mineral wool. See: Mineral Wool Guide.
K
K-Flex ST — Elastomeric foam by K-Flex. λ = 0.036 W/m·K, μ ≥ 7,000. See: Armaflex vs K-Flex.
Kingspan Kooltherm — Market-leading phenolic foam pipe insulation. λ ≈ 0.022–0.025 W/m·K — lowest of any commercially available pipe insulation. See: Phenolic Foam Guide, Foil-Faced vs Elastomeric.
L
Lambda value (λ) — Thermal conductivity (W/m·K). Lower = better. Armaflex EVO 0.033, K-Flex ST 0.036, Rocklap 0.034–0.040, Kooltherm 0.022–0.025. See: What Thickness Do I Need?
LTHW — Low Temperature Hot Water, up to ~90°C. Most common UK commercial heating system. See: Domestic Heating, BS5422 Explained.
M
Microban — Antimicrobial additive in Armaflex EVO. Inhibits mould and bacteria. Valuable in high-humidity environments. See: Swimming Pool Insulation.
Mineral wool — Non-combustible (A1) inorganic fibre insulation. No vapour barrier (μ ≈ 1). For high-temperature heating and steam only — not cold pipes. See: Mineral Wool Guide.
Mu value (μ) — Water vapour diffusion resistance factor. Higher = better vapour barrier. Armaflex EVO ≥ 10,000, K-Flex ST ≥ 7,000, Kooltherm foil > 100,000, polyethylene foam ~1,000–2,000, mineral wool ~1. See: Vapour Barriers.
N
Nominal bore — Conventional pipe size designation. Does not equal actual OD. 15mm nominal bore copper pipe = 18mm OD.
O
Open-cell foam — Foam with interconnected cells. Absorbs moisture, no effective vapour barrier. Polyethylene foam is open-cell. Not for cold pipes. See: Vapour Barriers.
Outside diameter (OD) — External pipe diameter in mm. Insulation bore sizes are matched to pipe OD.
P
Part L — Building Regulations requiring BS5422 minimum insulation thicknesses on new heating and hot water pipework. See: BS5422 Explained, Domestic Heating.
Phenolic foam — Rigid thermoset foam with ultra-low λ (≈ 0.022–0.025 W/m·K). Used with aluminium foil facing as vapour barrier. Key product: Kooltherm. See: Phenolic Foam Guide.
Polyethylene foam — Lightweight open-cell foam for domestic heating. No effective vapour barrier. Not for cold pipes. Products: Climaflex, Tubolit. See: Domestic Heating.
R
Relative humidity (RH) — Water vapour in air as % of maximum at that temperature. Higher RH = higher dew point = greater condensation risk. See: Vapour Barriers.
Rockwool Rocklap — Most widely specified mineral wool pipe insulation in the UK. Rock wool sections with aluminium foil and glass cloth facing. Up to +750°C, Euroclass A1. See: Mineral Wool Guide.
S
Self-seal — Elastomeric foam with factory adhesive strip on the longitudinal seam. Press firmly along the full length. See: How to Cut and Install.
T
Lambda value (λ) — See Lambda value above.
Trace heating — Self-regulating electrical heating cable for frost protection on critical exposed pipes. See: Outdoor Insulation.
V
Vapour barrier — Material layer resisting water vapour transmission. Required on all cold pipe applications. See: Vapour Barriers — Complete Guide.
W
Wall thickness — Thickness of insulation around the pipe (mm). Depends on pipe OD, service temperature, ambient conditions, and λ value. See: What Thickness Do I Need?, BS5422 Explained.
WRAS — Water Regulations Advisory Scheme. Approves products for contact with drinking water. Armaflex EVO carries WRAS approval. See: Cold Water Insulation.
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