Updated December 2025 by the Crib Goch Outdoor team — based on real wet-weather experience in Eryri.
When buying tents, jackets or camping gear, you’ll often see the term Hydrostatic Head (HH) thrown around. But what does it actually mean — and how waterproof is 2000mm, 5000mm or 10,000mm in the real world?
This updated guide explains HH in simple terms, how to compare ratings, and what level of waterproofness you really need for UK weather.
- Does a higher hydrostatic head mean better waterproofing?
- What Is Hydrostatic Head?
- What Is Considered Waterproof for Jackets?
- A Note on Paramo & Waterproof Ratings
- Why Hydrostatic Head Isn’t the Whole Story for Waterproof Jackets
- Hydrostatic Head Comparison for Tents:
- Real-World Implications: When Does HH Actually Matter with Tents?
- The Downsides of Very High Hydrostatic Head Ratings for Tents
- What Hydrostatic Head Rating Do You Actually Need?
- Final Takeaway
- Hydrostatic Head FAQ (Updated 2025)
What Is Hydrostatic Head?
Hydrostatic Head is a measure of how waterproof a fabric is. In testing, a column of water is placed on top of the fabric and slowly increased in height. The measurement (in millimetres) indicates how tall the water column can get before the fabric leaks.
So:
- 1000mm HH = leaks at 1 metre of water pressure
- 2000mm HH = leaks at 2 metres of water pressure
- 5000mm HH = leaks at 5 metres of water pressure, and so on.
This sounds unrealistic — you’re not standing under a two-metre pillar of water — but HH is actually a good way of simulating wind-driven rain, pressure from leaning, kneeling, or heavy downpours.
What Is Considered Waterproof for Jackets?
When it comes to waterproof jackets, hydrostatic head ratings need to be much higher than for tents.
Unlike a tent flysheet, a jacket is constantly exposed to:
- Shoulder-strap pressure from a rucksack
- Arm movement and fabric flex
- Wind-driven rain at speed
- Abrasion from rock, vegetation and pack contact
All of these dramatically increase water pressure on the fabric.
Realistically, in UK conditions:
- Below 5,000mm HH
• Not suitable for prolonged rain
• Likely to wet through under pack straps
• Only appropriate for emergency shells or dry-weather use - 6,000–10,000mm HH
• Entry-level waterproof jackets
• Fine for showers and short hill days
• May struggle in sustained Welsh rain - 10,000–15,000mm HH
• Suitable for regular UK hillwalking
• Handles pack pressure and steady rain
• Good balance of waterproofing and breathability - 20,000mm+ HH (or membrane equivalent)
• Proper mountain waterproofs
• Designed for prolonged rain, wind and exposure
• Typical of Gore-Tex, eVent and similar membranes
In short:
What’s “waterproof” for a tent flysheet is not waterproof enough for a jacket you’re moving in all day.
Hydrostatic Head for Jackets: A Quick Guide
| Use Case | Recommended HH |
|---|---|
| Emergency shell / dry weather | 5,000–6,000mm |
| General UK hillwalking | 10,000–15,000mm |
| Mountain & winter use | 20,000mm+ |
| High-output / all-day rain | Membrane-based systems |
| High-output / all-day rain | Paramo Directional Waterproofs |
A Note on Paramo & Waterproof Ratings
Not all waterproof clothing uses a membrane — and Paramo is the most well-known example of this.
Unlike traditional waterproof jackets (such as Gore-Tex or eVent), Paramo does not rely on a hydrostatic head–rated membrane. Instead, it uses a Directional Nikwax Analogy system, which works by actively moving liquid water away from the body rather than blocking it.
In simple terms:
- Membrane jackets stop water getting in using a waterproof barrier (measured in mm HH).
- Paramo garments move moisture outwards using a pump-liner system, even when the fabric is fully wetted out.
Because of this, Paramo jackets are not quoted with a hydrostatic head rating — and directly comparing them to a “10,000mm” or “20,000mm” jacket isn’t meaningful.
How Paramo Performs in the Real World
In prolonged UK rain — especially in places like Eryri, the Lake District and Scotland — Paramo is:
- Exceptionally good at staying comfortable when worn all day
- Very resistant to internal dampness caused by sweat
- Easy to maintain, as waterproofing can be renewed with Nikwax treatments
However:
- Paramo garments are generally heavier and bulkier than membrane shells
- They are less packable, making them better suited to wearing all day rather than carrying “just in case”
Why Hydrostatic Head Isn’t the Whole Story for Waterproof Jackets
Hydrostatic Head (HH) is a useful indicator of waterproofness — but for jackets, it’s only part of the picture. Two jackets with the same HH rating can perform very differently on the hill, especially in wet, windy UK conditions.
The Takeaway
Hydrostatic Head tells you how waterproof a fabric is —
but how dry you stay depends on the whole jacket.
For UK hillwalking and mountain use, prioritise:
- Good construction
- Fully taped seams
- Reliable DWR
- Sensible cut and fit
- Breathability that matches your activity
- Care, repair and re-proofing.
That’s why we always recommend choosing waterproof jackets based on use case and conditions, not just the biggest number on the label.
Hydrostatic Head Comparison for Tents:
1000mm HH
- Light showers
- Picnic shelters / fair-weather use
- NOT ideal for UK camping unless conditions are mild
2000mm HH
- Standard level for “waterproof” tents in the UK
- Handles heavy rain and wind
- The most common waterproof rating for general outdoor gear
3000–5000mm HH
- Better for sustained rain, strong winds and rough weather
- Recommended for UK campsites where weather is unpredictable
- Great for family tents and higher-pressure areas
5000mm+ HH (Groundsheets)
- Required for floors, because body weight dramatically increases water pressure
- Prevents seep-through when lying or kneeling on soaked ground
10,000mm HH and higher
- Used in expedition tents
- Handles sheeting rain, storms, and physical pressure on the fabric
- Often heavier and less breathable
- Overkill for most UK summer camping
Real-World Implications: When Does HH Actually Matter with Tents?
Hydrostatic Head is only one part of staying dry. In the hills around Eryri, other factors play a huge role:
1. Wind pressure
Wind pushes rain into the fabric, increasing pressure dramatically
2. Contact pressure
Leaning on a tent wall or kneeling on a groundsheet can exceed 2000mm easily, which is why floors need higher ratings.
3. Abrasion and ageing
A 5000mm tent that’s three years old may perform like a 2000mm tent if coatings have worn down.
The Downsides of Very High Hydrostatic Head Ratings for Tents
Reduced breathability
Thicker waterproof coatings trap moisture inside, especially in humid climates like Eryri. This can cause:
- Damp sleeping bags
- Condensation on tent walls
- Sweat build-up inside jackets
Increased weight
Higher HH fabrics are heavier — important for backpackers.
Stiffer handling
Some high-HH tents feel more rigid and harder to pitch or pack.
Higher cost
More advanced coatings = higher price, often unnecessary for fair conditions.
What Hydrostatic Head Rating Do You Actually Need?
Practical UK Guidance
| Use Case | Recommended HH |
|---|---|
| Summer festivals / fair-weather camping | 1500–2000mm |
| General UK camping | 2000–3000mm flysheet |
| Backpacking tents | 3000–5000mm flysheet |
| Any tent groundsheet | 5000–10,000mm |
| Hillwalking 3 Season jackets | 10,000–15,000mm |
| Mountain / winter jackets | 20,000mm+ or Paramo |
Balancing Waterproofness and Practicality
Choose a waterproof rating that:
- Matches the weather you expect
- Balances weight and packability
- Still allows breathability in humid UK conditions
More waterproof isn’t always better — it’s about appropriate protection, not marketing numbers.
Final Takeaway
Hydrostatic Head tells you how waterproof a fabric is but how dry you stay depends on the whole system.
For UK hillwalking and camping, prioritise:
- Sensible HH ratings
- Good design and construction
- Breathability
- Maintenance and reproofing
That’s how you stay dry in real Welsh weather — not by chasing the biggest number on the label (or lack thereof when it comes to Paramo). If you need any advice you know what to do… Contact Crib Goch Outdoor here
Hydrostatic Head FAQ (Updated 2025)
Is 2000mm waterproof enough for heavy rain?
Yes and No.
Yes — for tents 2000mm HH is generally enough for sustained heavy rain in the UK, especially when combined with good tent design and taut pitching. It’s the standard waterproof level for most 3-season tents. However, strong wind, ageing fabrics or poor seam sealing can reduce its real-world performance.
No – for jackets we consider 6000mm HH to be the absolute minumum and only suitable for lights showers. You should consider 10,000–15,000mm for a 3 Season waterproof jacket or 20,000+ for a mountain jacket where it takes a much higher Hydrostatic Head to be considered waterproof
Is hydrostatic head the same as waterproof?
Not exactly. Hydrostatic Head measures how much water pressure a fabric can withstand before leaking. A higher HH usually means the fabric is more waterproof, but factors like seam sealing, fabric age, condensation and pitch tension also affect how dry you’ll stay.
What’s a good hydrostatic head rating for tents?
For UK camping:
- Flysheet: 2000–3000mm is ideal
- Backpacking tents: 3000–5000mm for storm protection
- Groundsheets: 5000–10,000mm to handle sitting and kneeling pressure
Most reputable tents fall in these ranges for a reason — they strike the best balance between waterproofness, weight and breathability.
Do jackets use hydrostatic head ratings?
Jackets technically use a similar measurement, but the outdoor industry often reports waterproof membranes (like Gore-Tex or eVent) differently — usually quoted around 20,000mm+ equivalent. For walkers, the numbers matter less than the membrane quality and overall construction. Paramo for instance uses a different waterproof technology and measurement of waterproofness entirely, as it works in a different way
Does a higher hydrostatic head mean better waterproofing?
Yes — but with trade-offs. Higher HH fabrics are more waterproof but usually heavier, stiffer and less breathable. For most UK adventures, 2000–3000mm is more than adequate for tents and ~10,000mm for Jackets & Trousers
Why do ground sheets need a higher HH?
Because body weight massively increases water pressure. Kneeling on wet ground can easily exceed 3000mm, which is why groundsheets typically start at 5000mm to prevent seep-through.
Is 1000mm enough for light camping?
Only in very fair weather. 1000mm HH can handle light showers, but not prolonged rain or windy conditions. For camping in Wales, Scotland or the Lake District, 2000mm is a safer minimum.
Does a tent with higher HH last longer?
Not always. Durability depends more on fabric quality, coating, UV exposure and how well a tent is cared for. A 5000mm tent left in the sun for weeks can degrade faster than a 2000mm tent stored correctly.
Why does condensation occur even in a high HH tent?
Condensation is caused by humidity and temperature differences, not leaks. A tent can have a 10,000mm waterproof rating and still collect condensation if ventilation is poor.
