Types of adhesives are classified on four axes (how the adhesive sets, what polymer it forms, how it is delivered and what load it carries), and this reference sorts them into 14 adhesive types. Each adhesive type is a formulation of adhesive chemicals, grouped here by how the adhesive bonds and cures.
Physically setting types cool, dry or bond under pressure with no change, while chemically curing types polymerize by polyaddition, polycondensation or chain polymerization. Three quantities define the mechanisms: a pressure-sensitive adhesive (PSA) bonds when its storage modulus is below about 3 × 10^5 Pa at 25 °C and 1 Hz, a cyanoacrylate fixture time is the time to 0.1 N/mm² shear strength, and an amine-cured epoxy takes AHEW × 100 / EEW parts hardener per 100 parts resin. Two tables follow: one row per adhesive type with its key raw materials, and one row per sub-chemistry. A seven-step sequence then turns the classification into a choice.
Sources and checks: identities and hazard classifications are read at ECHA and the issuing regulator, standards at the body that publishes them, and grade values at the data sheet named next to them; methodology and fact-checking explains each step.
How Are Adhesives Classified?#
Adhesives are classified on four axes: setting mechanism (physically setting, chemically curing or combined), polymer nature (thermoplastic, thermoset or elastomeric), delivery form (100 % solids, solution, dispersion, film or powder) and load class (structural, semi-structural or non-structural). The axes follow the classification chapter of the Springer Handbook of Adhesion Technology, and no single axis classifies an adhesive alone. A styrenic block copolymer can base both a hot melt and a PSA, yet the two differ in setting, so each type is placed on all four axes, listed below.
- Setting mechanism: physically setting, chemically curing, or combined.
- Polymer nature: thermoplastic, thermoset, or elastomeric.
- Delivery form: 100 % solids, solution, dispersion or emulsion, film or tape, powder.
- Load class: structural, semi-structural, non-structural.
Physically Setting, Chemically Curing and Combined Adhesives#
Physically setting adhesives lose solvent or water, cool, or stay unchanged as PSAs; chemically curing adhesives polymerize by polyaddition (epoxy, polyurethane), polycondensation (phenolic, urea-, melamine-urea- and resorcinol-formaldehyde, silicone condensation, silyl-modified) or chain polymerization. Chain polymerization runs radically in acrylic, anaerobic and UV acrylate adhesives, anionically in cyanoacrylates and cationically in UV epoxies. A hot melt, as defined in EN 923:2015 (cited by IVK Technical Briefing Note 4, March 2015), is thermally melted, wets the substrate only while molten and develops cohesion by cooling.
Combined adhesives do both. Cure speed, temperature and by-products of each route are explained under how adhesives cure. A reactive polyurethane (PUR) hot melt first sets by crystallization of its polyester segments, then its free isocyanate groups cure with moisture to urea; dual-cure UV adhesives combine light cure with a second route. A reactive adhesive is therefore any chemically curing or combined system.
Thermoplastic, Thermoset and Elastomeric Adhesives#
Thermoplastic adhesives, such as ethylene-vinyl acetate (EVA) hot melts, polyvinyl acetate (PVAc), solvent polychloroprene and thermoplastic polyurethane (TPU), soften again on heating; thermoset adhesives, such as epoxy, polyurethane, phenolic and cured silicone, crosslink and do not. Epoxy is a thermoset: its oxirane rings react with the hardener into a crosslinked network.
Reactive hot melts cross the line. They are applied as thermoplastics and become thermosets once the moisture cure has crosslinked them after cooling. Elastomeric adhesives form the third class of the polymer-nature axis.
Classifying Adhesives by Delivery Form and Load Class#
100 % solids adhesives (hot melt, reactive liquids, UV-curing, cyanoacrylate) carry no carrier; solution and dispersion adhesives set as solvent or water leaves. ASTM D4800-94(2023), Standard Guide for Classifying and Specifying Adhesives, and ASTM D6465-99(2024), Standard Guide for Selecting Aerospace and General Purpose Adhesives and Sealants, sit among the ASTM adhesive standards for classifying adhesives. D4800 is a guide for classifying and specifying, not a tabulation system.
Load class separates structural, semi-structural and non-structural bonds. A structural adhesive carries design loads; its reactive thermosets are one- and two-part epoxies, toughened methacrylates and two-part polyurethanes.
Types of Adhesives by Chemistry: How Each Type Bonds and What It Contains#
Fourteen adhesive types make up this section: eight named for their chemistry, three for their delivery form (hot melt, water-based, solvent-based), one for its bonding behavior (pressure-sensitive) and two for a performance class (structural, conductive). The table compares their setting class, bonding or cure route and key raw materials, physically setting types first.
| Adhesive type | Setting class | How it bonds or cures | Key raw materials |
|---|---|---|---|
| hot melt adhesives | physically setting (cooling); reactive grades combined | applied molten, wets only while liquid, develops cohesion by cooling; PUR grades then moisture-cure | EVA, polyolefins, block copolymers, polyamides; tackifying resin; wax; antioxidant |
| pressure-sensitive adhesives (PSA) | physically setting (no phase change) | permanently tacky; bonds under light pressure when storage modulus is below about 3 × 10^5 Pa (0.3 MPa) at 25 °C (77 °F) and 1 Hz (Dahlquist criterion, 1969) | acrylic, SIS (styrene-isoprene-styrene) or SBS (styrene-butadiene-styrene), natural rubber, PIB (polyisobutylene) or silicone gum; tackifier; oil; crosslinker |
| water-based adhesives | physically setting (water loss) | water evaporates or is absorbed; particles coalesce into a film above the minimum film-forming temperature (MFFT) | PVAc, VAE (vinyl acetate-ethylene), acrylic, PUD (polyurethane dispersion) or latex dispersions; PVOH (polyvinyl alcohol), starch, dextrin or casein solutions; plasticizer |
| solvent-based adhesives | physically setting (solvent loss) | strength develops as solvent leaves the film; polychloroprene contact adhesives bond by autohesion and crystallization of trans-1,4 segments | polychloroprene, natural rubber, SBC (styrenic block copolymer), nitrile rubber or TPU; tackifier resin; solvent blend |
| epoxy adhesives | chemically curing (polyaddition) | oxirane rings react with amine, anhydride or latent hardeners to a crosslinked thermoset; amine dose phr = AHEW (amine hydrogen equivalent weight) × 100 / EEW (epoxy equivalent weight) | BPA or BPF (bisphenol A or F) epoxy resin, novolac; hardener; reactive diluent; toughener; fillers |
| polyurethane adhesives | chemically curing (polyaddition) | polyisocyanate and polyol form urethane links; one-part grades cure with moisture to urea, two-part grades are mixed | isocyanate or NCO (isocyanate group) prepolymer; polyether or polyester polyols; catalyst |
| cyanoacrylate adhesives | chemically curing (anionic chain polymerization) | surface moisture starts polymerization; fixture (0.1 N/mm², 14.5 psi shear strength) in seconds at 22 °C (71.6 °F) and 50 % RH (relative humidity); higher RH speeds cure; full resistance after at least 24 h (LOCTITE 401 TDS, February 2012) | alkyl 2-cyanoacrylate monomer; acidic and radical stabilizers; thickener; plasticizer |
| structural acrylic and MMA adhesives | chemically curing (radical chain polymerization) | two-part free-radical redox cure at room temperature, elastomer-toughened, strongly exothermic | MMA (methyl methacrylate) monomer; elastomer toughener; peroxide initiator such as benzoyl peroxide; activator |
| anaerobic adhesives | chemically curing (radical chain polymerization) | stays liquid in air; cures when oxygen is excluded between close-fitting metal parts, where iron and copper ions reduce the hydroperoxide | dimethacrylates or urethane methacrylates; hydroperoxide; accelerators; stabilizer |
| UV and light-curing adhesives | chemically curing (radical or cationic chain polymerization) | free-radical acrylate cure (oxygen-inhibited) or cationic epoxy cure (not oxygen-inhibited, dark cure continues); one substrate must transmit the light | urethane acrylate oligomer; acrylate monomers; photoinitiator |
| silicone adhesives | chemically curing (polycondensation or addition) | condensation cure with tin or titanate catalyst releasing acetic acid, oxime or alcohol, or platinum addition cure without by-product | silanol- or vinyl-terminated PDMS (polydimethylsiloxane); crosslinker silane or Si-H siloxane; fumed silica; catalyst |
| silyl-modified polymer adhesives | chemically curing (polycondensation) | moisture hydrolyzes alkoxysilyl end groups, which condense to a siloxane network and release methanol or ethanol | silane-terminated polyether or polyurethane; plasticizer; calcium carbonate; fumed silica; silanes; catalyst |
| structural adhesives | chemically curing (performance class) | reactive thermosets (one- and two-part epoxy, toughened methacrylates, two-part polyurethanes) that carry design loads | toughened epoxy, methacrylate or polyurethane systems |
| conductive adhesives | binder-dependent (performance class) | silver flake above the percolation threshold conducts in all directions (isotropic); sparse particles conduct only through the compressed thickness (anisotropic); ceramic fillers conduct heat but not current | silver flake; epoxy, acrylate or silicone binder; alumina, boron nitride or aluminum nitride |
The table condenses each type to one line; the type page carries the formulation, process window and data. The epoxy formula shows how a row turns into a number: diethylenetriamine (DETA) has an AHEW of 20.6 g/eq, so a resin of EEW 190 takes 10.9 phr DETA (calculated from the ECHA molecular formula).
Sub-Chemistries Within Each Adhesive Type#
24 sub-chemistry pages sit under 8 of the types, from EVA, polyolefin and reactive hot melts to threadlockers. The table names each sub-chemistry with its parent type and focus.
| Sub-chemistry | Adhesive type | Focus |
|---|---|---|
| EVA hot melt adhesives | Hot melt | vinyl acetate content, melt index, formulation |
| polyolefin hot melts | Hot melt | APAO and metallocene formulations |
| hot melt pressure-sensitive adhesives | Hot melt | styrenic block copolymer HMPSA |
| polyamide and polyester hot melts | Hot melt | high-temperature thermoplastic hot melts |
| reactive polyurethane hot melts | Hot melt | moisture cure and green strength |
| hot melt application | Hot melt | melt temperature, open time, equipment, char |
| acrylic pressure-sensitive adhesives | Pressure-sensitive | emulsion, solvent and UV-curable types |
| rubber-based PSAs | Pressure-sensitive | natural rubber and block copolymer formulas |
| silicone pressure-sensitive adhesives | Pressure-sensitive | MQ resin, cure systems, release |
| removable and repositionable PSAs | Pressure-sensitive | removable, repositionable, permanent |
| two-part epoxy adhesives | Epoxy | mix ratios, pot life, room-temperature cure |
| one-part heat-cure epoxy adhesives | Epoxy | latent hardeners, cure schedules |
| toughened epoxy adhesives | Epoxy | CTBN, core-shell rubber, crash-durable grades |
| high-temperature epoxy adhesives | Epoxy | Tg, novolac resins, service limits |
| two-part polyurethane adhesives | Polyurethane | isocyanate index, mixing, cure |
| moisture-curing polyurethane adhesives | Polyurethane | one-part moisture cure |
| waterborne PUD adhesives | Polyurethane | heat activation, crosslinking |
| threadlockers | Anaerobic | strength classes, fastener sizes, torque |
| optically clear adhesives | UV and light-curing | OCA and LOCA for displays |
| cationic UV-curing epoxy adhesives | UV and light-curing | cationic cure |
| PVAc and VAE emulsion adhesives | Water-based | formulation, water resistance |
| emulsion polymer isocyanate (EPI) wood adhesives | Water-based | two-component wood adhesive |
| contact adhesives | Solvent-based | polychloroprene chemistry, open time, bond formation |
| spray adhesives | Solvent-based | aerosol and canister lamination |
Why One Adhesive Can Belong to Two Types#
A reactive polyurethane hot melt is both a polyurethane adhesive and a hot melt: it is applied molten, sets by crystallization and cures with moisture. Structural adhesives form a class drawn from epoxy, structural acrylic and two-part polyurethane, with toughening that adds peel and impact resistance. Conductive adhesives are filled epoxy, acrylate or silicone binders, so one product belongs to its binder type and to the conductive class.
How to Choose an Adhesive Type: Substrate, Load, Temperature and Process#
Choose an adhesive type in seven steps, starting with the substrates and their surface energy and ending with compliance and cost, so that each step narrows the chemistries left for the next. The seven steps run in the order below.
- Identify the substrates and their surface energy.
- Define the load type and level.
- Set the service temperature and environment.
- Fix the process window: open time, set time, cure schedule, line speed and equipment.
- Check the gap and joint design.
- Confirm compliance: food contact, VOC, diisocyanate training and labeling.
- Compare cost.
Substrates come first because a liquid adhesive bonds only what it wets. The surface energy of the substrate decides whether a liquid adhesive wets it, as set out under surface energy of the substrate. Polypropylene and polyethylene show critical surface tensions of 30.5 and 31.6 mN/m in the Accu Dyne survey averages, against 37.5 mN/m for PMMA (polymethyl methacrylate), which is why low-energy plastics resist bonding.
The process window and compliance then remove types that fit the joint but not the line or the market. A one-part cyanoacrylate fixes in seconds, while a two-part epoxy needs a pot life and a cure schedule. Under REACH Annex XVII entry 74 (Regulation (EU) 2020/1149), industrial or professional use of diisocyanates at 0.1 % by weight or more is allowed since 2023-08-24 only after documented training. In the US, 21 CFR 175.105 lists food-packaging adhesive components with their conditions of use, and SCAQMD Rule 1168 (amended November 4, 2022; amendments proposed for a 4 December 2026 hearing) sets VOC limits for adhesives in its district.
How Adhesive Types Connect to Adhesive Raw Materials#
Every adhesive type is a formulation of raw materials from 15 families: base polymers, thermoset resins, tackifiers, plasticizers, waxes, curing agents, isocyanates and polyols, monomers, photoinitiators, adhesion promoters, fillers, solvents, antioxidants, functional additives and natural binders. Each family fills one formulation role, from the base polymer that gives cohesive strength to the tackifier that gives wetting and specific adhesion.
Physically setting thermoplastic types draw on tackifiers, waxes and oils, while chemically curing types draw on curing agents, isocyanates, monomers and photoinitiators. The 15 families of adhesive raw materials are compared on their own index. Adhesion promoters, fillers, antioxidants and functional additives cut across all types.
Each type page lists the substances of its formulation. The grouping follows the composition chapter of the Springer Handbook of Adhesion Technology: primary resins, solvents, fillers, plasticizers, reinforcements and additives.
Adhesive Types by Industrial Application#
Industrial applications such as packaging, labels, tapes, wood, automotive and electronics each draw on a different set of adhesive types. Packaging uses EVA and polyolefin hot melts, PVAc, VAE, starch and dextrin, plus two-part polyurethane laminating adhesives; labels use acrylic and rubber hot melt PSAs and casein or starch wet glues.
Automotive bonding relies on one-part toughened epoxy for the body in white and one-part moisture-cure polyurethane for glazing, and electronics on one-part heat-cure epoxy and UV acrylates. Which adhesive types each industry uses is set out under industrial adhesive applications, with footwear, hygiene, bookbinding, medical devices, aerospace and composites alongside.
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