Glossary of Heat Shrink Tubing Terminology
Adhesive Lined Tubing: Dual-wall tubing with an inner layer that melts and flows when heated, filling voids in the areas being covered, and forming a mechanical bond to the substrate.
Antifungal: Additive used to retard fungal growth in tubing, especially for applications in which tubing is exposed to damp environments.
Antioxidant: Additive used to prevent yellowing of tubing or loss of strength when exposed to oxygen in the atmosphere.
AWG (American Wire Gauge): A method of specifying conductor size. Lower gauge numbers indicate larger conductor size.
Brittleness Temperature: The temperature below which a flexible material exhibits brittle failure when subjected to a specified impact during testing.
Colorant: Pigment additives used to introduce color to tubing. Both natural colored opaque polymers and clear polymers can be colored. Addition of colorant to clear polymers results in a tinted transparent polymer.
Compound: A chemical blend of base resin and desired additives, which becomes the raw material from which tubing is extruded.
Concentricity: Used to describe the uniformity of the wall thickness of tubing, it is a measure of the offset of the center of the inside diameter from the center of the outside diameter.
Core: The inner wall of dual wall, heat shrinkable tubing.
Cross-linking: The formation of three-dimensional covalent bonds between molecular chains in a polymer, thereby improving the mechanical and thermal properties.
Durometer: A measurement of the hardness or resistance to surface penetration of a polymer. Usually measured using Shore or Rockwell scales. Higher numbers represent harder materials.
Elastic Memory: The ability of a polymer to be temporarily shaped to a different geometry before returning to its original shape upon the application of heat. This is the basic principle by which heat shrink tubing has been developed.
Elongation: The maximum amount, expressed as a percentage, that tubing can be stretched in length before it breaks.
Expansion: A process used to create heat shrinkable tubing in which polymer tubing is enlarged in diameter (and the wall thickness is reduced) under closely controlled thermal conditions, resulting in a product that will revert to the original diameter upon application of heat.
Expanded ID: The minimum internal diameter of heat shrinkable tubing as supplied to the customer, before heat is applied for recovery.
Extrusion: The thermal and mechanical process by which a polymer compound is conveyed through a heating chamber, forming dies, cooling tanks and vacuum tanks to form tubing.
Flame Retardant: An additive that is included in tubing compounds to improve resistance to burning.
Hardness: A measurement of resistance to surface penetration that correlates well with mechanical strength and rigidity. Usually measured using Shore or Rockwell scales.
Heat Shrinkable: Tubing that is capable of being reduced in size when exposed to heat. Heat Shrink Tubing
Jacket: The outer wall of dual wall, heat shrinkable tubing.
Lead Free Tubing: see European Union Directive, RoHS.
Liner: The inner wall of dual wall, heat shrinkable tubing.
Longitudinal Shrinkage: The change in length, as opposed to the change in diameter, of heat shrinkable tubing during the recovery process initiated by the application of heat.
MIL Spec (Military Specification): These are standards published by the U.S. Department of Defense. There are several Mil specs that apply to flexible tubing. These include MIL-I631, MIL-I-7444 (replaced by SAE-AMS-I-7444) and MIL-DTL-23053 (replaced by SAE-AMS-DTL-23053).
Monomer: A small molecule that bonds chemically with other monomers to form a longer chain polymer molecule.
OFT (Optional Flame Test): Former CSA test for measuring the flame retardance of tubing. This test is now obsolete and has been replaced with the VW-1 test.
Operating Temperature: The maximum recommended temperature at which tubing may operate in continuous service.
Plasticizer: A chemical additive that is included in polymer compounds to provide flexibility. Plasticizers serve to fill and increase the spacing between polymer chains, allowing them to slip past each other more readily. Types of plasticizers include phthalates; trimellitates; adipates; epoxidized vegetable oils, and polymerics.
Polymer: A compound consisting of long molecular chains formed from monomers occurring as repetitive "building blocks".
Polyolefin: A generic term for a group of polymers produced from olefin (or alkene) monomers. Olefins are hydrocarbon substances having a single carbon-to-carbon double bond. Polyolefin heat shrink tubing is typically made from polyethylene and is usually cross-linked.
Recovery (Heat Shrinkable Tubing): Heat activation of the elastic memory effect to cause expanded heat shrinkable tubing to return to its originally extruded size.
Recovered ID: The internal diameter of heat shrinkable tubing after being allowed to recover fully.
Recovery Temperature: The midpoint of the recovery versus temperature curve of heat shrinkable tubing.
Resin: The base material in a polymer compound.
Shore Hardness: A series of scales used to indicate hardness. The Shore A scale is most commonly used to measure the hardness of plastic tubing. Within a given scale, a higher number indicates a harder material.
Shrink Ratio: The nominal ratio of expanded diameter to recovered diameter of heat shrinkable tubing.
Specific Gravity: The ratio of the density (mass per unit volume) of a material to the density of water.
Strain Relief: The use of a length of tubing to reduce the stress or strain on a wire or cable being flexed.
Tensile Strength: The ratio of the amount of axially applied force required to break or rupture a piece of tubing to the cross-sectional area of the tubing. It is expressed in units of force/area, such as pounds per square inch (psi).
Thermoplastic: A polymer that can be repeatedly melted and solidified with only minimal degradation of the properties following each cycle. Common examples are polyvinyl chloride and polyethylene.
Thermoset: A polymer, such as polyolefin, in which irreversible chemical "curing" or "set" takes place as the molecule chains are cross-linked in three dimensions through covalent bonding. Once set, the polymer cannot be melted.
Ultraviolet Degradation: The loss of strength or discoloration caused by long-term exposure of tubing to sunlight or other ultraviolet rays.
Ultraviolet (UV) Stabilizer: An additive to tubing compounds that protects against loss of strength or discoloration when it is exposed to the outdoors.
VW 1: A flammability test conducted by UL or CSA. Tubing with a VW-1 rating is highly flame-retardant.
Additional Resources and Articles of Interest:
https://support.boshart.com/can-heat-shrink-splice-kits-be-used-in-underground-applications