Pertex® Fabric FAQ: Is the REI Pertex Quantum Jacket Waterproof? Plus 420D Oxford, ITY Knit & More

I work on the quality and compliance side of Pertex®. Before a fabric lot ships to an outdoor brand, I check it: roll length, weight, weave, finish, water-column results, labels. Roughly 250 lots a year. It isn’t glamorous work, but it keeps bad fabric out of good jackets.

These are the questions I hear most often, in roughly the order I hear them.

What is Pertex® fabric, exactly?

Pertex® is a fabric brand, not a fiber brand. The ® matters: it means the trademark is registered, so the name refers to specific engineered woven fabrics, not to every shiny nylon that feels similar. The range breaks down by job: Quantum for downproof, packable shells; Shield for waterproof-breathable shells; Equilibrium for active layers where breathability matters as much as protection.

Here’s the thing: the name tells you the family, not the performance. Two jackets can say Pertex® and use different weights, weaves, and finishes. That’s why my first question is always “Which Pertex, and what spec?” The logo starts the conversation; the spec sheet finishes it.

Is the REI Pertex Quantum jacket waterproof?

Short answer: no, not if “waterproof” means staying dry in an all-day downpour. Pertex Quantum is a lightweight woven nylon with a durable water repellent (DWR) finish. It resists wind, shrugs off light snow, and handles a short shower. Because the weave is tight, it also holds insulation in place. That makes it a nice choice for insulated jackets. It does not make it a membrane hardshell.

A product like the REI Pertex Quantum jacket is a good example: REI has used Quantum fabric on several own-brand jackets. The face fabric is exactly that—light, soft, weather-resistant, not a sealed waterproof layer. I can’t speak to the finished garment’s seam taping or zippers; that’s on the maker’s quality side. But when the product description says “water-resistant,” that wording is doing real work. Trust it.

Is 420D Oxford fabric waterproof?

Uncoated 420D Oxford nylon is not waterproof. The “420D” tells you the yarn weight—420 grams per 9,000 meters—and “Oxford” tells you the weave pattern. Neither of those blocks water. What blocks water is a coating, usually polyurethane.

A PU-coated 420D Oxford can handle rain, puddles, and general gear abuse; an uncoated one lets water through. So the real question is not “is 420D oxford fabric waterproof?” but “what coating does this specific fabric have, and what hydrostatic head did it test at?” That number, measured in millimeters per ISO 811, is the honest answer. I don’t have a single universal number for all 420D Oxford because mills coat them differently. Ask for the current lot’s test report. If the seller can’t provide one, that’s a red flag.

What is the ITY knit fabric definition?

ITY stands for interlaced twist yarn. The short ITY knit fabric definition: it’s a synthetic knit—usually polyester—made from twisted and interlaced filaments. The result is a fabric with a soft, dry hand, a slight crepe texture, good drape, and low wrinkling. You’ll find it in dresses, skirts, and warm-weather tops.

Does it belong in a technical-fabric conversation? Rarely. Pertex® is woven technical nylon; ITY is a knit fashion fabric. It won’t provide wind resistance, DWR, or downproofness. I’m not a knit specialist, so if you’re planning to engineer stretch and recovery, talk to someone who lives in knits. But for a quick definition, that’s it—and it should help you keep ITY out of outdoor shell discussions.

Is Pertex® similar to black vinyl upholstery fabric?

No. They both count as “coated or treated textiles,” and that’s where the similarity ends. Black vinyl upholstery fabric is usually a heavyweight furniture textile with a PVC or PU surface. It’s easy to wipe clean, very durable, and essentially not breathable. Pertex® is engineered for apparel and sleeping bags; it’s lightweight, breathable, compressible, and meant to move with a body.

A vinyl upholstery fabric makes sense on a chair. Pertex® makes sense in a jacket. Upholstery is outside my area, so I won’t pretend to advise on furniture grades. But the broader point is core quality work: end use decides what “good fabric” means. Pick the right category first; the brand name comes second.

Why would you reject an entire fabric lot?

Because “close enough” is expensive. In 2023, I rejected a coated lot that tested around 6,200 mm hydrostatic head when the contract specified 10,000 mm. The mill argued that 10,000 was overkill. Maybe it was. But the brand planned to label those jackets “waterproof,” and a maybe isn’t a material spec.

We sent the lot back. The rework cost time and money. It still cost less than a recall, a warranty wave, or a retailer pulling the product.

I’m not claiming I’ve never slipped. A few years ago, I skipped a retest on familiar greige from a known mill—same fabric, same finish, what could change? The finish had changed. A water-beading check caught it before the fabric shipped. Lesson learned: test the current lot, not the memory of the last one. Prevention is cheaper than correction. I keep that checklist close.

What is the cheapest quality improvement in fabric sourcing?

Write every critical spec into the contract before production starts, then inspect against those specs before the fabric is cut. The checklist I give smaller brands has six lines:

• Yarn and weave construction, plus fabric weight in g/m².
• Finish type: DWR, PU coating, or laminate.
• Hydrostatic head target per ISO 811 if water resistance is claimed.
• Shade band and roll-to-roll color consistency.
• Test report for the current lot, not last season’s data.
• Labeling and care instructions that match the actual finish.

Five minutes of verification beats five days of correction. That isn’t an empty slogan; it’s the formula that has cut our rework rate this year. Check early, check consistently, and make the supplier prove the fabric meets the spec.