Every figure below is taken from a resin manufacturer’s own processing guide or technical data sheet — BASF, DuPont, Celanese, Covestro, SABIC, Solvay, Lanxess, Victrex and others. Sources are listed at the bottom. Where two suppliers disagree materially, both numbers are shown rather than averaged, because averaging two vendors’ specs produces a number neither of them stands behind.
Always verify against the data sheet for the specific grade you are running. These are family-level typical values. Fillers, impact modifiers, flame retardants and colorants all move the numbers.
First: hygroscopic is not the same as hydrolysis-sensitive
This distinction explains why ABS tolerates 0.1% moisture while polycarbonate demands 0.02%, and it is the single most useful thing to understand about drying.
- Hydrophobic — PE, PP, PS, PVC. They pick up surface moisture only, which seldom exceeds 0.01%. Drying is usually unnecessary.
- Hygroscopic, cosmetic consequences — ABS, SAN, ASA, acrylic, PPE, POM. They absorb water and mold with splay if wet, but the polymer backbone survives. They tolerate 0.05–0.10%.
- Hygroscopic, performance consequences — PET, PC, nylon, PBT, TPU, PEI. Water at molding temperature cleaves the polymer chain. The damage is permanent and the limits are 0.02% or tighter.
Drying reference chart
Scroll the table sideways to see all columns →
| Resin | Hygroscopic? | Drying temp | Drying time | Target moisture | Notes |
|---|---|---|---|---|---|
| Nylon 6 (PA6), unfilled | Yes — performance | 176°F / 80°C | 2–6 h | 0.03–0.12% | BASF recommends 0.03–0.06%; Lanxess allows to 0.12%. |
| Nylon 6 (PA6), glass-filled | Yes — performance | 150–180°F / 66–82°C | 2–5 h | Scale by polymer fraction | 30% GF → 0.14%, 40% → 0.12%, 50% → 0.10%. See note 3. |
| Nylon 66 (PA66), unfilled | Yes — performance | 175–180°F / 80–82°C | 2–4 h from a fresh bag | 0.03–0.2% | BASF 0.03–0.06%; DuPont <0.2%, tightening to 0.1% above 600°F melt. |
| Nylon 66 (PA66), glass-filled | Yes — performance | 176–180°F / 80–82°C | 2–4 h, often longer | Scale by polymer fraction | DuPont: filled and impact-modified grades “may be longer.” |
| Nylon 11 / Nylon 12 | Yes, but low absorption | PA11 176–194°F / 80–90°C PA12 176–212°F / 80–100°C | PA11 ≥4 h PA12 2–4 h dehumidified | PA12 <0.1% | Arkema publishes no injection-molding limit for PA11. EMS caps dry air at 80°C — yellowing above. |
| Polycarbonate (PC) | Yes — performance | 248–250°F / 120–121°C | 2–4 h | ≤0.02% | Covestro tightens to 0.01% for optical and lighting parts. |
| PC/ABS | Yes — performance | 212–230°F / 100–110°C | 2–4 h; 4–6 h regrind or filled | 0.02–0.04% | Covestro says 0.02%, SABIC 0.04% — a genuine 2× disagreement. Use 0.02%. |
| ABS | Yes — cosmetic | 176–203°F / 80–95°C | 2–4 h | 0.1% general 0.02–0.05% plating | Moisture causes splay but does not cleave the backbone. |
| Acetal — POM homopolymer | Weak; toughened grades are hygroscopic | 176°F / 80°C | 2–4 h; toughened 4–8 h | Dry only above 0.2% Toughened <0.05% | Celanese: standard Delrin grades generally do not require drying. |
| Acetal — POM copolymer | Essentially no | 180–248°F / 82–120°C | 3–4 h | ≤0.1% | Celanese publishes no maximum for Celcon; can normally be molded as received. |
| PET — bottle / preform | Yes, strongly | 300–350°F / 149–177°C | 4–6 h | 0.005% (50 ppm) | Dew point −20 to −40°F. Crystallize amorphous regrind first — see note 4. |
| PET — injection grade | Yes — performance | 250–275°F / 120–135°C | 2–4 h virgin; 4–6 h regrind | <0.02% (200 ppm) | Above 0.02% strength drops with no visible surface defect. |
| PBT | Yes — performance | 250°F / 121°C typical (176–284°F / 80–140°C published) | 2–4 h | 0.02% | Some suppliers permit 0.04–0.05%. Drop to 200–212°F for overnight residence. |
| PEI (Ultem) | Yes — performance | 302°F / 150°C | 4–6 h; cumulative ≤24 h | 0.02% | SABIC caps total drying at 24 h. |
| PEEK | Not hygroscopic, but must be dried | 302–320°F / 150–160°C | 2–4 h | 0.02–0.05% | Victrex <0.02%, Solvay 0.05% — cite per brand. Tray depth ≤1 in. |
| PPS | Resin no; mineral fillers yes | 230–325°F / 110–163°C | 2–4 h | 0.02% | Widest published spread of any resin here — 50°C between suppliers. Follow your grade’s sheet. |
| PSU (Udel) | Yes — absorbs very rapidly | 275–325°F / 135–163°C | 2–4 h (shorter at higher temp) | 0.02–0.05% | Solvay 0.05%, BASF 0.02%. |
| PPSU / PES | Yes | 275–350°F / 135–177°C | 3–5 h | 0.02–0.05% | Absent from every dryer-OEM chart — use resin-maker data only. |
| TPU | Yes, strongly | 194–230°F / 90–110°C Aliphatic 104–140°F / 40–60°C | 1–4 h | <0.02–0.05% | Hardness- and chemistry-dependent. Use within 15–30 min of the dryer. |
| Acrylic (PMMA) | Yes — cosmetic | 158–208°F / 70–98°C | 2–4 h | <0.02% strict 0.05–0.1% non-critical | Grade-dependent. Röhm’s rule: 10–15°C below the Vicat softening point. |
| SAN | Mild | 175–176°F / 79–80°C | 2–4 h | 0.04–0.08% | Published as a range, not a maximum. |
| ASA | Yes — cosmetic | 176–194°F / 80–90°C | 2–6 h | 0.04–0.1% | SABIC 0.04%, Ravago 0.1%. Cumulative max 12 h. |
| Polystyrene / HIPS | No — surface moisture only | 160–167°F / 71–75°C, only if needed | 1–2 h; never >12 h | No published maximum | Dry only for regrind, humid storage or abnormal conditions. |
| PPO / PPE modified (Noryl) | Barely — saturates at 0.07% | 212–248°F / 100–120°C Noryl PPX 149–167°F / 65–75°C | 2–4 h; never >8 h | <0.02% | Noryl GTX has a two-sided window: too dry (<0.02%) also causes splay. |
| Polypropylene (PP) | No | 167°F / 75°C, cosmetics only | 2 h when required | Up to 0.2% has no effect | Filled and reinforced PP grades are moisture-sensitive. |
| Polyethylene (PE) | No | Not required | — | — | Warm-air surface-moisture removal only if condensation is present. |
| PVC (rigid and flexible) | No | 120°F / 49°C, optional | 2–3 h | Not specified | Most PVC compounds ship ready to process. |
| TPV (Santoprene) | Yes | 180°F / 80°C | 3 h virgin; 4 h with regrind | ≤0.08% | |
| COPE (Hytrel) | Yes | 210°F / 100°C | 2–3 h; not >12 h | 0.10% | Arnitel ≤0.05%. |
| Styrenic TPE-S | No | 140–175°F / 60–80°C, only if needed | 2–4 h | Not specified | Pre-drying generally unnecessary. |
Seven things the chart cannot tell you
1. Over-drying is a real defect
“When in doubt, dry longer” is wrong for several families. BASF prints on every Ultramid sheet that excessive drying “may lead to an increase of melt viscosity during processing.” DuPont: “Do not overdry; it will discolor the nylon.” SABIC caps Noryl at 8 hours and cumulative Ultem drying at 24. HIPS should not be dried beyond 12 hours. Toray warns that over-drying PPS causes plasticization and other failures.
2. The post-dryer window is 15 to 30 minutes
SABIC notes that for ABS, “as little as 15 minutes of exposure on a humid day can cause moisture defects.” Covestro limits unheated hopper residence for polycarbonate to 30 minutes. BASF says TPU should be used within 15–30 minutes. Covestro adds a subtler trap: conveying dried resin with cold atmospheric air re-wets it — convey with hot dry air off the dryer.
3. Glass-filled nylon needs a tighter number than its data sheet says
Glass does not absorb water, so a 0.2% reading on a 30% glass-filled grade means the polymer fraction is actually at 0.29%. Scale the limit by polymer content: 30% GF → 0.14%, 40% → 0.12%, 50% → 0.10%. Mike Sepe documented a 43% glass-filled PA66 molded at its data-sheet 0.2% losing 20% of its intrinsic viscosity.
4. PET regrind must be crystallized before it is dried
Amorphous PET goes tacky around 175°F and clumps; the clumps do not break up as temperature rises, and they bridge in the hopper and coat thermocouples. Crystallize first with mechanical agitation, then dry. Clear regrind is amorphous; white regrind is already crystalline. Crystallizing is not drying — recrystallized PET still has to be dried afterward.
5. Nylon goes dryer to press, with nothing in between
DuPont states that remote tray ovens with manual transfer to the hopper are “not recommended,” and that no more than one hour’s supply should sit in the hopper. Their exposure ladder is worth memorizing: a fresh bag needs 3 hours of drying, a bag left open several days needs 20, and regrind stored in non-moisture-proof containers needs 60. And never use a circulating or fresh-air oven — Lanxess warns that in the extreme case “the granules can contain more moisture after drying than they did beforehand.”
6. Regrind and colorant change the numbers
SABIC: doubling particle weight increases drying time roughly 60%. Regrind and glass-filled PC/ABS goes from 3–4 hours to 4–6. Santoprene goes from 3 hours to 4. And masterbatch should be tumble-blended with the resin before drying, not after — BASF, Covestro, ExxonMobil and Lubrizol all say so independently.
7. You may not be able to measure the tightest specs on your floor
Covestro’s assessment: no shop-floor weighing system can reproducibly determine residual moisture below 0.05%. Hitting 0.01–0.02% verifiably requires Karl Fischer or the carbide method. Analyzer setpoints are also resin-specific — Solvay specifies 200°C for standard PEEK but 224°C for PEEK XT, and 170°C for sulfones. A wrong setpoint gives a passing reading on wet resin.
A note on dryer-manufacturer charts
Conair, Wittmann, motan, Maguire and Labotek all publish resin charts, and they are useful cross-checks. Two cautions. Conair’s Carousel Plus chart has an “Initial Moisture %” column that is as-supplied incoming moisture, not a target — it is widely misread as a spec. And Maguire’s cycle times are in minutes because they are vacuum-dryer figures, not comparable to desiccant hours. When an equipment chart and a resin maker’s guide disagree, the resin maker wins.
BASF Ultramid and Ultradur processing data sheets · DuPont/Celanese Zytel & Minlon Molding Guide, Rynite PET Product Reference Guide, Hytrel Injection Molding Guide · Celanese Delrin Technical Molding Guide (2024), Celcon Processing & Troubleshooting Guide, Polyester Technical Manual · Covestro Injection Molding of High-Quality Molded Parts — Drying, Processing of TPU by Injection Molding · SABIC ULTEM Resin Processing Guide, NORYL Injection Molding Guide, Cycolac ABS and Cycoloy PC/ABS processing guides · LANXESS Processing data for the injection molder, Processing of Pocan PBT · Solvay/Syensqo Ryton PPS Processing Guide, KetaSpire PEEK XT Processing Guide, Sulfones Quick Molding Guide · Victrex Injection Molding Processing Guide (2022) · Evonik VESTAMID and VESTAKEEP processing guidelines · Arkema Rilsan PA11 · EMS-GRIVORY Guide Injection Molding · Polyplastics Molding Technology for DURACON POM · INEOS Styrolution Lustran and Luran S product guides · Teknor Apex acrylic and PVC processing guides · Röhm PLEXIGLAS product information · ExxonMobil/Celanese Santoprene injection molding guidelines · Lubrizol TPU Injection Molding Processing Guide · Asahi Kasei and INEOS polypropylene processing guides · Mike Sepe, Why (and What) You Need to Dry and What Is the Allowable Moisture Content in Nylons?, Plastics Technology.
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