A tarp needs to keep rain out, pitch properly and survive life in your pack. But what do 20D ripstop nylon, 210T polyester and PU 3000 mm actually tell you?
Read the specification in three parts: the fibre is the material, the weave is the construction and the coating provides waterproofing. Shape, seams and attachment points then determine how the finished shelter works over your sleeping spot.
This guide explains the terms and connects them to the decisions you make when choosing, pitching and caring for a tarp.
Reading a tarp specification
| Term | What it describes | Why it matters |
|---|---|---|
| Nylon or polyester | The fibre | How the fabric behaves |
| Ripstop | Reinforcement woven into the cloth | Resistance to a tear spreading |
| D, such as 20D | Yarn weight per unit length | Part of the balance between weight and durability |
| T, such as 210T | Thread count | How densely the fabric is woven |
| PU or silicone | The coating | Waterproofing and repair compatibility |
| Hydrostatic head, such as 3,000 mm | Resistance to water pressure | Waterproof performance in a fabric test |
Read these properties together. A single large number tells you little about whether a tarp suits your trip.
Nylon vs polyester
Nylon is widely used in lightweight tarps for its strength relative to weight. It stretches and absorbs more moisture than polyester. A nylon tarp may therefore sag when wet and need a gentle adjustment.
Polyester absorbs less moisture and remains more dimensionally stable when wet. That can be helpful when you want a pitch to change as little as possible through a rainy night. Yarn, weave and coating also affect the strength of the finished fabric. SlingFin compares nylon and polyester.
Compare the finished shelter’s weight, coverage and construction. Nylon does not automatically mean fragile; polyester does not automatically mean heavy.
What is ripstop?
Ripstop fabric has a grid of reinforcing yarns, often visible as small squares. The reinforcement is intended to limit the spread of a tear. It does not make the cloth impossible to puncture or rip. SlingFin explains ripstop construction.
Treat “ripstop” as a construction feature rather than a promise that a tarp can withstand any load. Look at the reinforced corners and attachment points too.
20D vs 210T: different measurements
D means denier, a measure of yarn weight per unit length. For the same material, a higher value means a heavier yarn.
T means thread count, combining the counts in both directions of the weave.
You cannot conclude that 210T is thicker or stronger than 20D by comparing those numbers. One fabric can have both a D specification and a T specification. MSR explains denier and thread count.
Also check what a quoted weight includes. A 350 g tarp and a 455 g shelter including guylines, pegs and a bag can be the same product.
What is a PU coating?
PU stands for polyurethane. On a tarp, it is a polymer coating that makes the woven cloth waterproof. Polyester with a PU coating means polyester fibres plus a separate coating: polyester and polyurethane are different materials.
PU is common in tents and tarps and can provide a surface suitable for seam taping. Silicone is another waterproof coating. Sil/PU usually means silicone on one side and PU on the other; sil/sil means silicone on both sides. SlingFin explains fabric coatings.
The practical lesson is to consider the fabric and coating together. “Nylon” alone does not tell you which adhesive or sealant will bond to its surface.
Silnylon, silpoly and seam sealing
Silnylon refers to silicone-treated nylon; silpoly refers to silicone-treated polyester. Check whether the opposite surface also has PU, as that matters for repairs.
Silicone-treated surfaces need a sealant that bonds to silicone. PU-compatible products and silicone sealants are not interchangeable. On a fabric with different coatings, the side you repair matters too. GEAR AID explains how to choose a seam sealer.
Seam sealing is a separate job: it treats a seam where water can enter rather than spraying the entire tarp. If a new Momo Jord tarp leaks, contact us so we can help identify the cause.
What does 3,000 mm hydrostatic head mean?
Hydrostatic head measures resistance to water pressure. A 3,000 mm rating represents the pressure from a three-metre column of water in a test. It is not a limit on the amount of rain that can fall during your trip. Sea to Summit explains hydrostatic head.
A higher rating cannot replace suitable dimensions or a good pitch. Waterproof cloth will not stop rain blowing around an edge. Check how far the shelter extends beyond your hammock and whether you can lower the windward side.
When pitching, give water a clear route off the tarp, distribute tension across the guylines and adjust any pockets where water collects. Shape and setup are part of weather protection too.
What does an aluminised lining do?
An aluminised inner surface has a thin metallised layer that reflects radiant heat. This is the silver surface inside Momo Jord’s Large Tarp and Winter Tarp. It is different from insulating fill and from a water-repellent treatment.
The Winter Tarp’s end flaps help keep out wind-driven rain. An underquilt provides insulation beneath the hammock. The reflective surface is an additional property of the fabric, rather than a replacement for those other elements. Read about the Winter Tarp.
Momo Jord tarp materials in practice
| Tarp | Fabric and waterproofing | Construction |
|---|---|---|
| Asym Tarp Ultralight | 20D ripstop nylon, silicone/PU, 3,000 mm | Asymmetrical shape; 350 g tarp weight |
| Large Tarp | 210T polyester, PU, 3,000 mm, aluminised inner | Larger rectangular shelter; 800 g tarp weight |
| Winter Tarp | Same fabric as the Large Tarp | Closable end flaps; 825 g tarp weight |
The Large Tarp and Winter Tarp differ principally in shape and coverage. The Asym Ultralight uses a lighter fabric and provides a more open shelter. Choose according to what you want to carry and how much of your sleeping area you want to enclose.
Do tarps need waterproofing spray?
A new Momo Jord tarp comes coated and ready to use. You do not need to apply waterproofing spray first.
A water-repellent treatment, often called DWR — Durable Water Repellent, helps droplets bead and roll off. The waterproof coating stops water passing through the cloth. Reduced beading does not necessarily mean that the tarp leaks. Nikwax explains repellency and waterproof coatings.
We do not recommend a fixed reproofing schedule. If performance changes, start by finding out what has happened. Improving repellency, sealing a seam and restoring a damaged coating are different jobs. GEAR AID describes PU coating restoration.
Condensation or a leak?
Moist air meeting cold fabric can form condensation underneath. Droplets may have formed there rather than passed through the tarp. Ventilation can help, although it will not prevent condensation in every condition. MSR explains condensation.
| What you notice | What to check |
|---|---|
| Droplets spread across the underside | Condensation and airflow; open the ends when conditions allow. |
| Water appearing repeatedly at one point during rain | A seam, hole or local damage. |
| Wetness near the ends of the hammock | Coverage and rain blowing in. |
| A pocket of standing water | Pitch angle and the distribution of guyline tension. |
| Sticky or peeling coating | Fabric condition before choosing a treatment. |
Use the table to begin troubleshooting. Photos of both the complete pitch and the place where water first appears can help identify the cause.
Keeping your tarp in good condition
Dry it before storage. PU coatings can deteriorate through hydrolysis, a reaction with moisture accelerated by heat. Store your tarp somewhere cool and dry; do not leave it damp in its bag between trips. SlingFin explains storage and coating life.
Clean gently. Start with water and a soft sponge. Use a suitable cleaner if necessary, avoid machine washing and fabric softener, and let the fabric dry completely afterwards. MSR’s cleaning guidance.
Check before the next trip. Inspect guylines, attachment points and seams. Distribute the load when pitching. If the cloth flaps, start with the angle and setup before pulling everything tighter.
When comparing tarps, begin with three questions: How much coverage do I need? How much do I want to carry? How do I want to pitch it? Understanding the materials helps you choose a shelter that suits your nights outdoors.
