Cling film is lightweight and waterproof... both in the real world... and any other worlds! The trouble is, it's not very comfortable, durable or practical, nor is it breathable in any sense of the word. Calling something 'water resistant' covers a multitude of things... but it best describes something that might let some water run off for a short while, but in the end it will get wet or leak quite badly.
You can have proper waterproof fabric, that won't let a drop of water through, but basically ruin it by blasting stitch-holes all over it, covering it in seams and attaching logos, until it leaks like a sieve. Unless stitch-holes are sealed, items made of waterproof fabric won't actually be waterproof when you use them.
if you were wet under the straps "and other regions" then it may well be perspiration? Did the fabric of the mica wet out or did it bead? If you were in rain pretty much constantly then the humidity will have been pretty high and this in turn will have reduced breathability.
Was the jacket zipped up all the time or were you able to vent it from time to time? If it was done up then you'd be hotter and perspiring more and the jacket might not have been able to cope/breathe enough to keep you dry.
No jacket is totally waterproof I don't think. It strikes me that the breathability might be the issue rather than waterproofing. If you are walking and carrying a pack then you are likely to be perspiring and this may be the reason for your being wet under the jacket.
Were you only wet in areas where the jacket was in contact with the pack? The straps and your back?
Did you enjoy the walk?
There's a very good piece on waterproofs on Andy Kirkpatrick's website: The truth About Waterproof Breathable fabrics.
I know the Mica is a lightweight jacket: I'm surprised it let you down so badly.
Good that you enjoyed the wild camping though!
Waterproof, there's a can of worms (or perhaps a bucket of eels)...
Let's start with the pack. Most packs are made of waterproof material, but that's not the same as a waterproof pack, because the material is joined at seams and they will generally leak. There are exceptions, with all the seams welded, but these are quite unusual (e.g., Ortlieb's packs) and unless you're quite sure you have such an exception then you want either a pack cover or a waterproof liner. I much prefer the latter, even in a waterproof pack, because if you have a waterproof pack and you put your wet overtrousers and jacket in when the rain stops then the waterproofing is just keeping all that water inside. If you have a liner then the dry stuff stays in that and any wet stuff, water bottles etc can go outside the liner but still in the pack.
Next, on to waterproofs. Generally the case that any day you spend in continuous rain you're going to get wet, because even if the rain is kept out there's perspiration from inside and it doesn't really have anywhere to go once the outside of the waterproof is wet through (that's not leaking, but it stops any vapour from perspiration getting out, and straps will stop that too).
Try it an an older non-breathable cag and you'll soon appreciate that some breathability is a lot better than none! You're in a small, closed system where keeping the outside water out makes it difficult (pretty much impossible over several hours) to deal with the perspiration being generated inside. The high humidity you'll encounter on a rainy day doesn't help: think of how much more windows mist up on rainy days.
You've other problems in all-day rain, which is any water getting in to your mid-layers around the big holes (sleeve cuffs, hem and neck) will wick through the inner garment and travel along the fibres. Over enough time this will make innards quite wet though the waterproof outer layer is not technically leaking. If that sounds bad then look at a paddler's or diver's dry suit and see what genuinely waterproof seals are like... you really don't want to walk up a hill with that sort of thing!
Just to be very clear - by design/specification etc the mica is totally waterproof.
(Absent the universal caveats above of course.).
The outer fabric on anything will wet out under rain, and especially so in places under tension like the shoulders etc - or is that down to the angle the rains hits at? Not sure.
Its the membrane underneath which should then stop water ingress. Sadly it will also block water vapour on the way out.
Further testing, if you have a suspicious spot on something that should be notionally waterproof suspend the garment so it makes a bowl you can pour water in to, with the bit you think is leaking at the bottom. Pour in water so the garment makes a bucket with clear space underneath, and wait...
it's entirely possible you'll get a mist of water over the outside, which is just moisture condensing out of the air against a surface that conducts heat well, but if you get continuous dripping from the base after a while you have a leaking fabric.
Kate, I have waterproof jacket and trousers. Where can I get a grey tee-shirt from?
It doesn't have to be grey, but grey's just a really easy colour to see damp patches on.
But I like these t-shirts, and some of them are grey
I know, I can wear my fish shirt.
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