A pair of overtrousers only earns its place if you actually put them on.

Most of them stay in the rucksack.

On an open hillside in wind, that is not laziness. Getting into most pairs means balancing on one leg, and on many of them it means unlacing a boot first.

So the thing that decides this purchase is the side zip, not the waterproof rating.

For a wet day in Eryri the Montane Cetus is the pair to buy. Every figure below is quoted from the maker’s own product page, read on 14 September 2026.

The links to Amazon on this page are affiliate links. Buy through one and the site takes a small commission, and what you pay stays the same.

The three at a glance

Read the second column first. It is the one you will be grateful for, standing in the rain at Bwlch Glas.

Overtrousers	Side zips	Waterproof rating	Breathability	Weight
Montane Cetus	AquaGuard side zips, length not given on the UK page	20,000mm	RET under 7	320 g
Berghaus Deluge 2.0	Three-quarter length, with snap fasteners	12,000mm	18,000 G/M2/24hrs	0.374 kg
Regatta Pack-It	None listed	Not published	10,000 g/m2/24 hours	Not published

Montane Cetus Waterproof Pants

Best for anyone walking Welsh hills through the autumn and winter.

Montane Cetus Waterproof Pants 20,000mm hydrostatic head, RET rating under 7 320 g, AquaGuard side zips, hems adjust over boots Read the full specification on Amazon

What Montane publishes for them:

• A 20,000mm hydrostatic head, in a three layer PETRICHOR fabric
• A RET rating of less than 7, which Montane says suits high output activity
• A stated weight of 320 g
• AquaGuard side zips, and an elasticated hem that adjusts over boots
• BARRIER treatment at the openings and hems, which Montane says stops water wicking in

That 20,000mm is the highest figure published on this page. Regatta publishes no figure at all, so the three cannot be ranked on this line alone.

One point of detail is worth having straight.

Montane’s UK page names the AquaGuard zips without giving their length.

The same pants on Montane’s US site are listed with a three-quarter length YKK AquaGuard side zip.

That is long enough to clear a boot.

Where it is the wrong choice: if the pair will live in the car for occasional light rain. It is the most specified of the three, and the one you pay most for here.

Berghaus Deluge 2.0 Pant

Best for a handful of Welsh hill days a year, with the zips still there when you need them.

Berghaus Deluge 2.0 waterproof overtrousers 12,000mm hydrostatic head, 18,000 G/M2/24hrs Three-quarter length side zips with snap fasteners Read the full specification on Amazon

Berghaus publishes this:

• A hydrostatic head of 12,000mm
• Breathability of 18,000 G/M2/24hrs
• A weight of 0.374 kg
• Three-quarter length side zips and snap closures
• An elasticated waist with side adjustment, and articulated legs
• Hydroshell 2L fabric, a polyamide shell with a polyurethane coating

Berghaus describes the zips as ideal for ventilation and for what it calls no-fuss changing. That second use is the one this page is about.

The rating sits below the Montane and is the second of the two figures published here.

One thing Berghaus does not say anywhere on that page is whether the seams are taped. The gap is worth knowing about rather than guessing at.

Where it is the wrong choice: if you are out in weather most weekends. The Montane publishes a higher rating and a lower weight.

Regatta Pack-It Overtrousers

Best as the emergency pair that lives in the rucksack from March to October.

Regatta Pack-It waterproof overtrousers ISOLITE 15000 fabric, taped seams Packs away into its own stuff sack Read the full specification on Amazon

Regatta publishes this much:

• ISOLITE 15000 fabric, 100% polyamide, at 80 gsm
• A breathability rating of 10,000 g/m2/24 hours
• Taped seams
• An elasticated waist, unlined, with two side pocket openings
• Packs away into its own stuff sack

Regatta gives no hydrostatic head figure for these, and no weight. ISOLITE 15000 is the name of the fabric on that page, not a rating in millimetres.

There is also no side zip in the feature list. That means sitting down and taking your boots off, whatever the ground is like.

That is a real cost on a mountain and a small one on a valley path.

This pair works best as the spare you carry and hope not to need.

Where it is the wrong choice: as the only pair you own for the tops. Taped seams are good, an unstated rating and no zip are not.

What the side zip is actually for

A zip long enough to clear a boot is the difference between putting the trousers on and deciding not to bother.

The British Mountaineering Council gives the rule in one line. “It’s easier to be able to pull them on and off while your boots are on, so make sure there are zips down the sides.”

Think about where you will use them.

Rain on Snowdon rarely starts in the car park.

It starts twenty minutes up, in wind, on a slope with nowhere dry to sit. A three-quarter zip turns that into a thirty second job, standing up.

A pair with no zip means kneeling in the wet to unlace a boot first.

That is why walkers finish the day wet, with dry overtrousers still in the bag.

What the numbers mean on a wet day

Hydrostatic head is a laboratory measure.

It records how much water pressure a fabric holds off before it lets water through.

No maker on this page says what figure is enough for a mountain, and this page will not invent one.

What the two rated pairs publish is 12,000mm and 20,000mm. The gap between them matters far less than whether the trousers are on your legs.

Breathability is the trap here. Berghaus quotes 18,000 G/M2/24hrs and Montane quotes a RET rating of less than 7.

Those are two different scales, and they cannot be ranked against each other. A lower RET number means more breathable, while a higher G/M2 number means the same thing.

On a hill you want numbers you can act on, not adjectives.

The same applies to a specification sheet. Zip length and weight will change your day more often than the fourth digit of a rating will.

When you do not need to buy a pair

If your walking is valley paths and the lower lakes, and you turn back when it looks grim, the trousers in your wardrobe will do.

Wet legs on a low path are uncomfortable. Wet legs on an exposed ridge in wind are how people get cold fast.

If you are new to the hills, the question behind this is usually a simple one.

Is this one more thing you have to buy before a first big walk?

Overtrousers are not, for a summer walk up the Llanberis Path in a settled forecast. They become one the moment you go higher, later in the year, or with children who cannot warm themselves up by walking faster.

The British Mountaineering Council writes that “a waterproof outer layer of jacket and trousers will help to keep you dry”.

It names both halves, and the trousers are the half most walkers leave at home.

The pair for your kind of walking

If you are out in Welsh weather most months, buy the Montane. The highest published rating here, the lowest published weight, and zips that clear a boot.

If you walk the hills a few times a year, buy the Berghaus. Three-quarter zips and a 12,000mm rating cover everything Snowdonia will do to you on a walking day.

If you want a spare to carry all summer and rarely open, buy the Regatta. It packs into its own sack and is the cheapest of the three.

Keep it for that job and not for the tops.

Whichever you buy, the zip is what you are paying for, because it is what makes you put them on while you are still dry.

The jacket half of this decision has its own answer in what actually keeps you dry on a Welsh hill. The rest of the list sits in what to pack for a day in Snowdonia.