Xylene
Xylene (mixed isomers)
- CAS
- Formula
- C₈H₁₀
- Boiling pt
- ~137–144 °C
Used forEpoxy and polyurethane thinner, primer solvent and cleanup.
Buy urethane grade (low water) when it will touch isocyanate systems.
Full profileSolvents dissolve resins, set application viscosity and control how a film flows and dries. Choosing one means balancing solvency, evaporation rate, flash point, VOC rules and compatibility with the chemistry.
A solvent’s job ends when it leaves the film, but how it leaves decides how the coating looks. Fast solvents such as acetone and MEK flash off quickly to speed drying but can trap bubbles or cause dry spray. Slow solvents such as PMA and xylene keep the film open so it can level, at the cost of longer tack-free times. Most formulas blend several to shape the evaporation curve.
Chemistry compatibility comes first. Isocyanate systems need “urethane grade” solvents free of water and alcohols, because both react with NCO groups; esters, ketones and aromatics are common choices. Epoxies tolerate alcohols and glycol ethers, which often improve flow.
Regulation shapes modern formulas. VOC limits, expressed in grams per liter, push manufacturers toward high-solids and waterborne products and toward VOC-exempt solvents such as acetone, PCBTF, tert-butyl acetate and dimethyl carbonate under US EPA rules. State and local rules can be stricter.
Aromatics, ketones, esters, alcohols and VOC-exempt options, with boiling points for quick comparison.
Used forEpoxy and polyurethane thinner, primer solvent and cleanup.
Buy urethane grade (low water) when it will touch isocyanate systems.
Full profileUsed forFast solvent in lacquers, adhesives and some primers.
Faster and more hazardous than xylene; increasingly replaced in coatings.
Full profileUsed forCleanup and fast-dry solvent in low-VOC formulations.
VOC-exempt under US EPA rules but extremely flammable (flash point about −20 °C).
Full profileUsed forEpoxy and urethane cleanup, vinyl and acrylic lacquers.
Strong active solvent; also used for solvent-rub cure checks (ASTM D5402).
Full profileUsed forLow-VOC replacement for xylene and toluene in industrial coatings.
Evaporates at a rate similar to xylene while being exempt from US EPA VOC calculations.
Full profileUsed forLow-VOC thinner for urethane and epoxy coatings.
Exempt at the US federal level, though some state and local air districts still count it.
Full profileUsed forReference solvent for 2K urethanes and nitrocellulose lacquers.
Defines the evaporation-rate scale: n-butyl acetate = 1.0.
Full profileUsed forSlow, flow-promoting solvent for 2K polyurethane and epoxy finishes.
Improves leveling and reduces solvent popping in thicker films.
Full profileUsed forSurface wipe-down, waterborne cosolvent and epoxy cleanup.
Never thin isocyanate systems with alcohol: its –OH reacts with NCO.
Full profileUsed forLow-VOC alternative to acetone and MEK in coatings and cleaners.
VOC-exempt under US EPA rules since 2009; still flammable.
Full profileUsed forViscosity reducer in polyurea A-sides; equipment cleanup.
Very low volatility and odor, and compatible with isocyanates.
Full profileSolvency follows the old rule of “like dissolves like.” Aromatic solvents handle epoxy and alkyd resins; ketones and esters are strong, polar solvents for urethanes and acrylics; alcohols and glycol ethers help waterborne and epoxy systems. Formulators use solubility parameters to predict which blend will dissolve a resin.
Evaporation rate is measured relative to n-butyl acetate (= 1.0); higher numbers evaporate faster. The flash point is the lowest temperature at which vapors can ignite, and many common coating solvents flash well below room temperature.
The chart shows approximate relative evaporation rates for common coating solvents.
Approximate values; published figures vary slightly by source and grade.
A quick compatibility guide. Always use the solvent the manufacturer specifies on the TDS.
| Solvent class | Polyurethane / polyurea | Epoxy | Acrylic / lacquer | Notes |
|---|---|---|---|---|
| AromaticsXylene, toluene | Yes, urethane grade | Yes | Yes | Classic choices, but listed as HAPs in the US |
| KetonesAcetone, MEK | Yes, dry grades | Yes | Yes | Fast; acetone is VOC-exempt |
| Estersn-BuAc, t-BAc, PMA | Yes, preferred | Yes | Yes | Urethane-grade staples |
| AlcoholsIPA | No: reacts with NCO | Yes | Some | Fine for epoxy and wipe-downs |
| Exempt specialtiesPCBTF, DMC | Yes | Yes | Yes | Help meet VOC limits |
| CarbonatesPropylene carbonate | Yes, A-side diluent | Limited | Limited | Very low volatility |
Most coating solvents are flammable, and their vapors are heavier than air, so they can travel along floors to distant ignition sources. Inhalation and skin absorption add health risks.
Always follow the product’s Safety Data Sheet, your employer’s safety program and local regulations. This page is general reference information, not a substitute for them.
US EPA excludes certain compounds with negligible photochemical reactivity, such as acetone, PCBTF, methyl acetate, tert-butyl acetate and dimethyl carbonate, from VOC calculations. They are still flammable and may be treated differently by states and local air districts.
Alcohols contain –OH groups that react with isocyanate, consuming hardener and leaving a soft, under-cured film. Use the urethane-grade solvent specified on the TDS.
Evaporation rate, measured relative to n-butyl acetate. Fast solvents speed drying but can trap bubbles or cause dry spray; slow solvents improve flow and leveling but extend tack-free time.
The lowest temperature at which a liquid gives off enough vapor to ignite near a flame. Acetone’s is about −20 °C, so it is flammable even in winter conditions.