How We Compare Bivvies
Every bivvy on WhichBivvy is measured against the same standardised spec sheet. No recycled manufacturer blurb, no guesswork, no copying old listings without checking them. Here is exactly what we look at, why each spec matters, and how we verify the numbers.
What We Measure and Why
Hydrostatic Head (HH)
Why it matters: This is the single most important waterproofing spec on any bivvy. Measured in millimetres, it tells you how much water pressure the fabric can withstand before it starts to leak. A column of water 5,000mm tall pressing on the fabric should not get through. In practice: 5,000mm handles light to moderate UK rain, 10,000mm handles heavy sustained rain, 20,000mm handles everything a British winter throws at it, 25,000mm is about as good as it gets on any shelter currently on the market.
How we verify it: We check the manufacturer spec sheet first, then cross-reference with multiple UK retailers. Where figures conflict between sources we use the manufacturer figure and note the discrepancy. We also flag where HH ratings have changed between model years on the same product name.
Width
Why it matters: The external width measured across the front of the bivvy. This is the spec that determines whether your shelter will actually fit your swim. Narrow pegs, tight margins and overgrown banks all make width a critical consideration. Manufacturers measure from different points, which is why we standardise to external front width across every bivvy in the database.
How we verify it: We use the manufacturer listed external width. Where manufacturer and retailer figures conflict we use the manufacturer figure. We note where a bivvy has a significantly different rear width to front width as this affects usable internal space.
Depth
Why it matters: The external depth measured from the front of the bivvy to the back. Combined with width, this tells you the actual footprint on the bank. Depth determines how far back your bedchair can sit and how much storage space you have in front of you. A bivvy that is wide but shallow gives you a different fishing experience to one with serious depth.
How we verify it: We use external depth figures from the manufacturer. Some manufacturers quote internal depth which is always smaller. We flag where this distinction is unclear and adjust accordingly.
Height
Why it matters: The external apex height at the tallest point of the bivvy. This is the spec that determines whether you can sit upright on your bedchair and whether getting in and out at 3am requires the flexibility of a gymnast. Even a 10cm difference in height makes a noticeable difference in practice. Taller anglers should pay particular attention to this one.
How we verify it: We use the manufacturer apex height. Some manufacturers also quote front door height which is always lower than apex height. We list apex height as the primary figure and note door height separately where it is significantly different.
Weight
Why it matters: This is where bivvy specs get the most inconsistent. Some manufacturers quote bivvy-only weight. Some quote total system weight including pegs, groundsheet, storm cap and carry bag. The difference can be several kilograms. We standardise to bivvy-only weight wherever possible and clearly note what is and is not included in the quoted figure.
How we verify it: We check the manufacturer spec sheet for clarity on what is included in the quoted weight. Where this is unclear we cross-reference with retailer listings and note any discrepancy. We always flag where total system weight differs significantly from bivvy-only weight.
Setup Type
Why it matters: How the bivvy goes up. This is one of the most significant buying decisions and it is often undersold. Quick-erect shelters use a centre boss system that fans out in seconds with no pole threading. Pole and frame bivvies take longer but often reward you with more usable internal space and a more rigid structure. Brolly systems are the fastest of all but the least weatherproof. The right setup type depends entirely on how you fish.
How we verify it: We categorise each bivvy into one of four types: Quick-erect, Pole and frame, Brolly system, or Pop-up. Where manufacturers use different terminology for the same design we standardise to our categories.
Material
Why it matters: The fabric construction tells you a lot about how a bivvy will perform in the real world. Polyester is the most common material and handles moisture well. Nylon is lighter but less durable over time. Branded fabrics like Aquatexx, Dura-Stop and VenTec EX are proprietary constructions with specific performance characteristics. Denier count tells you how thick the individual fibres are, higher denier generally means more durable but heavier.
How we verify it: We use the manufacturer listed material specification. Where proprietary fabric names are used we include the manufacturer description. We note where material specification has changed between model years as this directly affects waterproofing and durability.
Capacity
Why it matters: Listed as the number of anglers the bivvy is designed to accommodate. One man means one bedchair comfortably. Two man means two bedchairs with enough room to live in. In practice a 1 man bivvy often has enough space for a solo angler to store all their kit alongside them. A 2 man bivvy fished solo gives you serious living space on a long session.
How we verify it: We use the manufacturer listed capacity. We note where a bivvy is described as "1 man plus" or similar as these are often closer to a 1.5 man in practice.
Model Year
Why it matters: This one catches people out more often than any other spec. The same product name can refer to significantly different shelters across different years. The Nash Titan Hide XL went from 5,000mm HH to 10,000mm HH between versions. The Fox Frontier became the Frontier II with completely redesigned features. If you are comparing specs you need to know which year you are looking at.
How we verify it: We verify model year against the manufacturer product page and note the specific year in the database. Where a retailer is clearly selling an older version under a current product name we flag this. We maintain separate database entries for different model years of the same product where specs differ significantly.
What Is Included in the Box
Why it matters: This affects the true cost of owning a bivvy more than any other single factor. Some bivvies come with groundsheet, pegs, storm poles, storm cap and carry bag all included. Others ship as a bare shelter with everything sold separately. A bivvy that looks cheaper on paper can end up costing significantly more once you have bought all the accessories you need to actually use it.
How we verify it: We list what comes in the box based on manufacturer specifications. Where retailers and manufacturers differ on included items we use the manufacturer figure and note any discrepancy. We flag where essential accessories like groundsheets and infill panels are sold separately.
WhichBivvy Rating
Why it matters: Our overall score out of 10. This is a weighted assessment that takes into account waterproofing, build quality, value for money, ease of setup, internal space and how well the bivvy delivers on its stated purpose. A lightweight budget shelter and a full-season premium system are judged against different criteria, we are rating each bivvy on how well it does what it sets out to do, not just comparing everything against the same absolute standard.
How we verify it: Ratings are assigned by the WhichBivvy team based on research, user feedback and where possible first-hand testing. We update ratings when new information becomes available or when a product is revised. We do not accept payment to improve a rating.
Our Data Process
We go to the manufacturer product page first for every spec. Not the retailer, not a forum post, not a comparison site that copied a comparison site. The manufacturer page is the primary source.
We cross-reference every spec against at least two additional sources. Where figures conflict we investigate the discrepancy, use the manufacturer figure, and note the conflict in our database.
Specs change between model years and manufacturers do not always shout about it. We review our database regularly and update entries when changes are confirmed. Model year is always listed so you know exactly which version you are looking at.
Our Independence
WhichBivvy is funded by affiliate commissions. When you click through to a retailer and buy a bivvy, we may earn a small commission at no extra cost to you. This is how we keep the lights on.
Our affiliate relationships do not influence our ratings, our spec data or our verdicts. A bivvy that pays us a higher commission does not get a higher rating. A brand that does not have an affiliate programme does not get ignored. If you spot something that does not look right, get in touch.