Why does hot melt glue string, and how do I stop it?
Stringing ("angel hair") usually means the glue is cutting off poorly at the nozzle: the nozzle is too far from the work, the glue is too cool and viscous, the substrate is cold, the nozzle tip is damaged or charred, solenoid air pressure is low, or a draft is blowing on the bead.
Sources: H.B. Fuller Hot Melt Troubleshooting Guide; Henkel, "Preventing stringing in hot melt packaging adhesives"
Symptom / Cause / Fix
| Symptom | Cause | Fix |
|---|---|---|
| Fine threads trail from the bead onto the box surface | Nozzle too far from the substrate [HBF-TS] [HEN-STR] | Bring the nozzle closer (H.B. Fuller: ideally 1/4 in) [HBF-BP] |
| Strings thicken, bead looks "ropey" | Glue temperature too low / viscosity too high [HBF-TS] [HEN-STR] | Increase temperature slightly, staying within the adhesive's recommended operating range [HBF-TS] [HEN-STR] |
| Stringing worse first thing in the morning or in winter | Cold board or paper [HBF-TS] [HEN-STR] | Allow substrates to adjust to ambient temperature before gluing [HBF-TS] [HEN-STR] |
| Strings appear even at correct temperature | Damaged or charred nozzle tip, poor cut-off [HEN-STR] | Check the nozzle tip is not plugged and in good condition; check filters and hoses for char [HEN-STR] |
| Gun drips or snaps slowly | Low air pressure to the solenoid [HBF-TS] | Ensure incoming air pressure is greater than 50 psi; inspect muffler buildup [HBF-TS] |
| Strings blow sideways | Fan or air-conditioning draft on the bead [HEN-STR] | Shield the glue area from direct airflow [HEN-STR] |
Fine threads trail from the bead onto the box surface
Strings thicken, bead looks "ropey"
Stringing worse first thing in the morning or in winter
Strings appear even at correct temperature
Gun drips or snaps slowly
Also check: if the gun drips between beads, H.B. Fuller lists worn nozzles, module faults and low air pressure as causes [HBF-TS].
Common follow-up questions
What is "angel hair" in hot melt gluing?
It is the thin strands of hot melt pulled away from the nozzle when the glue does not separate cleanly. The strands float through the air and land on equipment and products.
How close should the nozzle be to the board?
H.B. Fuller recommends that the applicator is not too far from the substrate, ideally 1/4 inch (about 6 mm).
Can a worn nozzle cause stringing?
Yes. Henkel notes that damage or char on the nozzle tip prevents the valve from operating properly, which leads to poor cut-off.
Related questions
- Why is my hot melt glue not sticking?
- Hot melt nozzle clogging and charring: what to do
- Hot melt vs cold glue (PVA) for rigid boxes
Gluing rigid boxes with hot melt by machine
Zhishang hot-glue models apply hot melt and pressure-sensitive glue with a 3-10MM glue line. Glue nozzles carry lifetime repair and trade-in replacement [ZS]. Working air pressure is 0.6MPa [ZS].
Inline with a box line or auto lid-and-base machine
Inline 4-Axis Hot Melt Gluing Machine for Rigid Boxes
- Effective size
600*600*130MM/50*50*25MM - Glue line width
3-10MM
Larger boxes at a standalone workstation
4-Axis Cabinet Hot Melt Glue Dispensing Machine
- Effective size
900*600*150MM/50*50*10MM - Glue line width
3-10MM
Hot glue to replace double-sided tape
3-Axis Cabinet Hot Melt Glue Dispensing Machine
- Effective size
900*600MM/50*50MM - Glue line width
3-10MM
Moving hot melt gluing from hand guns to a machine?
Send us your box size and glue. Prices are quoted per configuration. Specifications are for reference only; final specifications are subject to our quotation.
Request a QuoteWhatsAppReferences
- [HBF-TS] H.B. Fuller, Hot Melt Adhesives Troubleshooting Guide (PDF): Stringing, Dripping Nozzle
- [HBF-BP] H.B. Fuller, Packaging Adhesive Best Practices (PDF): stringing / angel hair
- [HEN-STR] Henkel, Preventing stringing in hot melt packaging adhesives
- [ZS] Zhishang product brochure p.02 (nozzle warranty), p.06, p.08, p.10 (hot-glue models)
Last updated: 2026-10-13