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Last Saturday you were working your project at Longdong. The sloper at the crux slipped no matter how you held it, and by the third go it felt like grabbing soap. On Wednesday evening a friend sends a photo: same route, someone sent it first go, with the caption "so dry today".
This is post 6 in the Climbing Mental Game and Tactics series. Post 5 on redpoint and projecting broke a route into sections, linked them, and set up an attempt plan. One question is left: which day should the send attempt go on? This post covers where friction comes from, and how to read the weather and decide whether this weekend is worth it.
The short version: friction comes from four things together, skin, chalk, rock and shoe rubber. Weather doesn't "change" friction directly. It works through your sweat, moisture on the rock and how soft your skin gets. What you control is how you use chalk, which day you go, and which wall you climb at what time.
Where friction comes from: four things
| Source | What you control | Where this post covers it |
|---|---|---|
| Skin | Sweat, how wet or dry your skin is, fingertip pad thickness | Here: how weather affects sweat. Skin care is in post 7 |
| Chalk | How much, whether old chalk has built up on holds | Next section |
| Rock | Which crag, which aspect, waiting for the rock to dry | The "Weather" and "Taiwan" sections |
| Shoe rubber | Clean soles, which shoe | The "Shoe rubber" section |
One skin study is worth knowing first. Bourne et al. (2011) had 15 climbers pull on a 2.8 mm sandstone edge. How hard they could pull correlated with fingertip pad thickness (r=.65), not with their force on bigger edges. The authors suggest that small holds depend on more than strength: they also depend on whether skin can deform and bite into the rock. The correlation showed up only on the 2.8 mm edge, not on deeper ones. This is also why the state of your skin decides how many goes you get in a day.
For Taiwan's crags and their rock types, see Taiwan's crags and rock types. This post is only about conditions.
Chalk: why the studies contradict each other (research + coaching consensus)
Does chalk actually work? The first studies gave opposite answers:
- Less friction: 15 people pressed a fingertip on sandstone, granite and slate and pulled sideways. With chalk, the friction coefficient was lower (Li et al. 2001). The authors suggest chalk dries and hardens the skin and leaves a layer of grains that roll between finger and rock.
- More friction: 11 experienced climbers hung on a fingerboard that slowly tilted until they slipped. With chalk, the friction coefficient rose 18.7% on limestone and 21.6% on sandstone (Amca et al. 2012).
- Same friction, better performance: For 19 climbers, chalk made no difference to the friction coefficient, but they hung longer with it: 62.9 s against 49.3 s on average (Kilgas et al. 2016).
A hold fitted with sensors showed one key detail: chalk on the hand alone raises friction; chalk on both hand and hold lowers it (Fuss and Niegl 2012).
A 2024 study from the University of Sheffield ties these together (Clarke et al., published online 2024; the main tests used one participant). They tested dry fingers and simulated sweaty fingers on four rock types and proposed a possible mechanism, which they label as such:
- A thin layer of chalk fills the tiny bumps of skin and rock and increases contact.
- Too much chalk turns into a "solid lubricant" layer that shears easily. That is the slip Li 2001 saw.
- Chalk makes friction more consistent across conditions, so one go isn't sticky and the next greasy.
- To the authors' surprise, chalk helped dry fingers more than simulated sweaty ones.
Clarke's paper also notes that climbers' habit of brushing holds between attempts fits the "fresh thin chalk works best, built-up chalk slips" mechanism, but brushing itself has not been tested. So the two tips below combine the proposed mechanism with coaching consensus. They are not results from controlled trials:
- Thin layer, little and often (coaching consensus). Chalk until you can't see a solid white coat. Don't plunge your whole hand into the bag.
- Brush the holds (coaching consensus). Before a go on your project, brush the key crux holds clean of old chalk and skin.
Something to do tonight: clip a brush to your harness. Next time, brush the two or three key crux holds before you try. When you chalk, touch only your finger pads, then tap off the excess.
Weather: the lab and the coaches disagree
Across 42 test sessions, there was no correlation between the friction coefficient and humidity or temperature (Amca 2012). The authors themselves say other factors are needed to explain the weather's effect. Yet every coach and climber will tell you: humid days are greasy.
Here are both sides:
| Claim | Source | Evidence level |
|---|---|---|
| In the lab, temperature and humidity didn't directly change finger-rock friction | Amca 2012 | Research |
| Heat itself doesn't make rock slick; sweat is what makes you fall. A little sweat adds friction; once you can see sweat, you're past the point | Climbing magazine's friction explainer (2021) | Popular-science summary |
| Above about 70% relative humidity, holds that look dry get wet after a go or two | Gripped (2024) | Media summary / climber experience |
| A few cold days followed by a warm, wet front is the classic recipe for condensation: the rock is still cold and the air is warm and humid | Mountain Project thread | Climber experience |
A possible way to reconcile them (inference; no study tests it directly): lab tests are short, a few seconds of finger pressure. A real attempt lasts minutes, and weather works through three routes:
- How fast you sweat. When it's hot and humid, sweat can't evaporate, and your hands get wetter as you climb.
- Condensation on the rock. When the rock is colder than the dew point, water condenses on its surface. Taiwanese climbers call this 反潮.
- Skin water content. A whole day in humid heat leaves your skin soft and thin, and each go hurts more.
Point 3 leads into the next post on skin care.
What is the dew point? Cool air down and at some temperature its water vapour starts to condense. That temperature is the dew point. The rule of thumb from the Mountain Project thread: if the rock is colder than the dew point, the rock sweats. So of two days with the same humidity, the one where the air is warmer than the rock (say, a sudden warm-up after a cold snap) is worse.
Something to do tonight: open your weather app, find "relative humidity" and "dew point", and add both to the list you check the day before a send attempt. Taiwan's Central Weather Administration (CWA) has an hourly page for the Keelung station (in Mandarin) with temperature, wind and relative humidity.
Shoe rubber: no test behind "0–5°C is best"
You'll often read that climbing-shoe rubber is stickiest at 0–5°C. Climbing magazine's friction explainer gives 32–41°F but cites no source. We searched research databases and found no experiment measuring climbing-shoe friction at different temperatures. So for now it's a saying, not a fact. It matters little in Taiwan anyway: winter at Longdong rarely drops below 5°C, and it drizzles often.
Another common claim is "softer rubber is stickier". Elkington et al. (2024) tested several climbing-shoe rubbers on granite and found softer rubber was not consistently better: grip depends on hardness, surface roughness and adhesion together.
What is certain is that sandy, dusty soles slip. At a sea-cliff crag, wiping your soles with your palm or a towel before you start is the cheapest fix there is.
Something to do tonight: put a small towel or a mat in your crag bag. Next time at Longdong, stand on it and wipe your soles clean every time before you tie in.
Taiwan: humidity is the norm, good days are events
Start with the numbers. According to the CWA monthly means (in Mandarin; select 相對濕度 "relative humidity", 1991–2020 normals, accessed 2026-10-19), Keelung's monthly mean relative humidity sits around 72–80% all year, and even the driest month, July, is 71.9%. We found no long-term average for Longdong itself, so the nearby Keelung station stands in for it.
Keelung monthly mean relative humidity (%, 1991–2020)
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 78.5 | 79.5 | 79.0 | 77.4 | 77.4 | 76.9 | 71.9 | 73.6 | 75.3 | 75.6 | 77.1 | 76.6 | 76.6 |
Set that against Gripped's point that holds get wet within a go or two above about 70% humidity, and the north Taiwan coast is on that line almost every day on average. So in Taiwan, good conditions are a weather event, not a season: the day or two when dry, cold air passes through and humidity drops.
The climber blog Kateberry (2018) (in Mandarin) recorded days like this: two dry days in March 2018, on the 18th and the 24th. On the 18th she wrote that it was "the first time I felt what dry means, it makes a huge difference". On the 24th humidity at Longdong dropped to 50–60%, and the Golden Valley area was packed with a queue on every route. That month she sent her first 5.12 at Longdong.
Season table
| Months | Weather | Effect on climbing | Source |
|---|---|---|---|
| Oct–Apr | Northeast monsoon, strongest Dec–Feb; the north and northeast get overcast skies and drizzle, with a cold front about every 5–7 days | Longdong is cold and damp, and the rock is often wet; the Northeast Coast scenic area office warns that swell is common Oct–Mar and asks people to stay off the shore | CWA monsoon explainer, Northeast Coast NSA Longdong page (both in Mandarin) |
| Mar–May | Home-improvement articles say condensation peaks | Shaded walls may sweat on warm days after a cold front (inference) | Searchome (2024) (in Mandarin; a home-design article, not a weather source) |
| Mid-May–mid-Jun | Taiwan's plum rain: stationary fronts bring persistent rain | Wait for the front to clear and the rock to dry | CWA climate: plum rain (in Mandarin) |
| Late Jun–Aug | Stable weather, mostly afternoon thunderstorms; Keelung's mean July high is 33.3°C | Lowest humidity of the year, but hot and sweaty; pick walls the sun hasn't reached yet, or hasn't hit for several hours | CWA plum-rain page, CWA monthly means |
| From mid-Aug | Typhoon season | Stay off the coast before and after a typhoon; for wind carrying spray and salt onto the rock, see "Rock sweating and salt on sea cliffs" | CWA plum-rain page |
| Sep–Nov | November is the north's driest month, but the northeast has its wettest stretch after autumn begins | Dry in Taipei doesn't mean dry at Longdong; check the northeast coast forecast | CWA climate: autumn (in Mandarin) |
The Longdong guide site climbstone.com says summer is 33–37°C, hot and humid, and January–March is rainy but climbable on dry days. It also says "Spring and fall can be wonderful", and good days come in any season.
Winter: head to Guanziling
The Central Mountain Range blocks the northeast monsoon, so the southwest gets far fewer rainy days than the northeast (CWA monsoon explainer). Many northern climbers skip Longdong in winter and go to Guanziling in Tainan instead: Kateberry writes that in winter she "holed up at Guanziling to focus on projects". For Guanziling's rock and rules, see Taiwan's crags and rock types, which also notes that Guanziling is humid in summer.
Rock sweating and salt on sea cliffs
What Taiwanese climbers call 反潮 is the dew-point problem above: warm, humid air meets a colder surface and condenses. The Searchome home article says it peaks in March–May and in the mountains and by the sea. Applied to the crag (inference): for a day or two after a cold front, when it warms up and a southerly picks up, the shaded, colder parts of a wall may feel damp even without rain.
Sea cliffs add salt. A UKClimbing forum thread discusses why sea-cliff rock sometimes feels soapy. One poster with some geology background explains that salt carried up by spray attracts water and needs more sun, wind or low humidity to dry than fresh water does. Another says wind blowing in from the sea is worst, and wind from inland is better. British instructor Libby Peter's sea-cliff notes say the same: sea cliffs get greasy from damp air alone, no rain needed, so let the sun hit the crag before you do. These are all climbers' experience; we found no research on Longdong or sea salt specifically.
Something to do tonight: on Thursday evening, check the weekend forecast for four things: ① whether a cold front or dry, cold air is coming through; ② whether relative humidity will drop below 70%; ③ whether the wind is onshore or offshore; ④ the CWA swell alerts and live sea conditions (both in Mandarin). Item ④ is a safety gate, not a bonus: if there's a swell alert, don't go to the coast, however good the other three look. The Northeast Coast scenic area office also warns that swell is common during the northeast monsoon (Oct–Mar) and asks people to stay off the shore, and clear days after a cold front fall in exactly that period. With no swell alert and at least two of the first three looking good, make it a send day.
Is this weekend worth it?
Here's the post boiled down to one table. It is coaching consensus plus inference, not a formula:
| You see | Call |
|---|---|
| A cold front has passed, skies are clearing, humidity has clearly dropped, and there's no swell alert | Go for it. This is a good Longdong day |
| Humidity 70–80%, but an offshore wind and sun | Worth going; put the send attempt after the sun hits the wall |
| Several cold days, then a sudden warm-up with an onshore wind | Shaded rock may sweat; work sections, or go to a crag away from the sea |
| A swell alert, or big seas during the northeast monsoon | Stay off the coast; go to Guanziling or the gym |
| Midday in summer, the wall has been baking all morning | Switch to a wall the sun hasn't reached, or hasn't hit for several hours (for example, an east-facing wall in the evening); a wall that baked all afternoon is still hot after the sun leaves |
The last row comes from Climbing magazine's article on climbing in the heat. The author says rock absorbs heat and stays hot for hours after the sun leaves, so on summer nights he picks east- or north-facing walls that haven't seen sun for a few hours. A wall the sun has only just reached is often better than one that just went into shade after baking for hours. He also rests in the shade between goes, because once his body heats up his fingers start to sweat.
Something to do tonight: next to your project notes (the attempt plan from post 5), add a "conditions" column. After each go, write down the date, time of day, humidity and how the holds felt. After a few sessions you'll know which conditions suit this route.
The gym in summer
Taiwan's gyms get muggy in summer too. We found no measured humidity data for Taiwanese gyms, so what follows is this series' suggestion / inference, with Climbing magazine's advice for the second point:
- Pick your time. The air-con keeps up and it's quieter on weekday mornings or late evenings. When it's packed, there's more body heat and more chalk dust in the air.
- Cool down between goes. Climbing magazine's friction explainer says resting somewhere cool and not letting your body overheat cuts sweating; some boulderers bring a small fan to blow on their fingers.
- Pick your routes. On sweaty days, save slopers and friction-dependent lines for better conditions. Climb big holds and steep lines, or do endurance volume.
Something to do tonight: next gym session, bring a small fan or a folding fan. Blow on your fingers between goes and note whether the holds feel different.
Practice: four scenarios
1. Before every go on your project you plunge your whole hand in the chalk bag until your palm is white, and the crux sloper still slips.
Answer
Too much chalk may be part of the problem. Clarke 2024 proposes that a thin layer fills the bumps and adds contact, while excess chalk becomes a slippery lubricating layer. Fuss and Niegl 2012 also found friction dropped when both hand and hold were chalked. Chalk only your finger pads, tap off the excess, and brush the crux holds before you try.
2. The forecast for Saturday says 78% relative humidity, 24°C, and the wind turning onshore from the east. Last week was cold all week; Saturday suddenly warms up.
Answer
Two risks stack up here. First, condensation: the rock is still cold and the air has turned warm and humid. Second, salt: wind off the sea carries salt and moisture onto the rock. Don't schedule the send attempt for this day. Work sections, or wait for the next pulse of dry, cold air.
3. It has been sunny in Taipei all week, so you've arranged to go to Longdong at the weekend.
Answer
Check the northeast coast forecast first. The CWA autumn page is clear: November is the north's driest month, but the northeast has its wettest stretch after autumn begins. Dry in Taipei doesn't mean dry at Longdong.
4. A weekend in July, you reach Longdong at noon. The sun has been on the wall all morning and the rock is hot to the touch.
Answer
July is Keelung's least humid month, but also the hottest, so sweat will be the main problem. Climbing magazine's heat article warns that sun-baked rock stays hot for hours after the sun leaves. Rest in the shade first and climb on walls facing away from the sun. Put the send attempt in the evening, and pick a face the afternoon sun hasn't hit.
Next
Even in good conditions, it's often your fingertips that give out first. Humid heat means more sweat and soft, thin skin; by the third go your pads are red, or a whole flap tears off. Post 7 on skin care covers sweaty hands, splits and flappers, and how your skin decides how many goes you get in a day.
References
- Li FX, Margetts S, Fowler I. Use of 'chalk' in rock climbing: sine qua non or myth? (J Sports Sci, 2001)
- Amca AM, et al. The effect of chalk on the finger-hold friction coefficient in rock climbing (Sports Biomech, 2012)
- Kilgas MA, et al. The Effect of Magnesium Carbonate (Chalk) on Geometric Entropy, Force, and Electromyography During Rock Climbing (J Appl Biomech, 2016)
- Fuss FK, Niegl G. The importance of friction between hand and hold in rock climbing (Sports Technology, 2012)
- Clarke BP, et al. The effectiveness of chalk as a friction modifier for finger pad contact with rocks of varying roughness (Proc IMechE P, 2024)
- Bourne R, Halaki M, Vanwanseele B. Measuring lifting forces in rock climbing: effect of hold size and fingertip structure (J Appl Biomech, 2011)
- Elkington T, et al. Sticky feet: a tribological study of climbing shoe rubber (Sports Engineering, 2024)
- How Much Chalk Is Optimal and What's The Perfect Temp For Rock Shoes? (Climbing, 2021)
- How to Maximize Your Climbing Performance in the Heat (Climbing, updated 2026-06)
- Understanding rock climbing conditions (Gripped, 2024)
- How to determine whether steep rock will "sweat" based on weather data? (Mountain Project forum, 2019)
- Why does sea cliff limestone get 'soapy'? (UKClimbing forum, 2023)
- Libby Peter: Sea-cliff essentials (PDF)
- Central Weather Administration: monthly means (in Mandarin; select relative humidity and mean maximum temperature, Keelung 1991–2020, accessed 2026-10-19)
- Central Weather Administration: swell alerts (in Mandarin)
- Central Weather Administration: live sea conditions (in Mandarin)
- Central Weather Administration: Keelung station observations (in Mandarin)
- CWA popular science: the monsoon (in Mandarin)
- CWA climate information: plum rain (in Mandarin)
- CWA climate information: autumn (in Mandarin)
- Northeast and Yilan Coast National Scenic Area: Longdong climbing area (in Mandarin; accessed 2026-10-19)
- Long Dong climbing information (climbstone.com)
- Kateberry: sending 非常不方便 (2018) (in Mandarin)
- Searchome: home damp-proofing and condensation (2024) (in Mandarin)
- Taiwan's crags and rock types
- Post 5: redpoint and projecting
- Post 7: skin care