We agree to differ then. However I do know that the outer material did not absorb any significant amount of water or allow any water through under a low static pressure.
My ND roof has, from new, always been bone dry, soaking wet or covered in snow depending on what the weather has been doing to it at the time. The only treatment it has ever had is the application of a hopepipe soak and gentle scrub with a moderately stiff brush. Always completely dry on the inside.
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I got on really well with the Renovo range for the mohair roof on my NC.
I primarily redid mine because it had faded a little.
I used the “Fabric Soft Top Cleaner”, followed by the “Soft Top Reviver” (which contains a black dye), followed by their “Ultra Proofer”.
Looks like new now and water still beads nicely 18 months after application. Only minor complaint was that the fabric was quite stiff for a while after application, which made the roof less compliant to put down, but it eased up after a bit.
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I’m old school, I use Fabsil+UV (not Gold) twice a year on my mohair roof, after scrubbing it gently with Johnson’s blue Baby Bath, rinsing and drying it off. I apply it with a wide paint brush, two coats at 90 degrees to each other, then keep it dry for 24 hours (I don’t rub it down after application as others have suggested). I’ve never had issues with streaks or marks.
The water repellancy is pleasing but that’s not why I do it, the car is kept outside and it protects it from UV, darkens it a bit and stops dirt binding to it so readily, especially bird muck. The waterproofness comes from the rubber/plastic layer membrane beneath the cloth.
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I have had mine since new, I don’t think water ever beaded off the roof on the occasions it got wet. I have however now applied Fabsil Gold, two coats as the instructions.
No issues whatsoever with markings, brushstroke marks or the like.
I did follow a logical process when applying though, completing “panels” boarded by the seams. RHS then LHS, lower window panel working to the front.
The roof was cleaned before hand and absolutely bone dry before I started. My heart was in my mouth.
Once dried I couldn’t tell it had been done. Which was a good thing.
My roof is Burgundy.
In this picture the RHS panel has been done (it was dry to the touch), I had just finished around the window and the main roof was still to be done.
A few days later …… it rained
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Perfect.
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Hi Matt, Just did mine last week. Used Renovo, , found it very good. A one litre bottle will do it 3 times. Make sure it is spotless and dry… I washed mine with gentle washing up liquid. Apply with a 2" brush seems to work ,but you need to work it in. not just spread it about., Start in the centre and work outwards , keeping a wet edge. splashes on glass or paint just wipe off with a damp cloth… Do not apply in direct sun, will dry too quickly. Do not shake bottle , pour into a container and stir gently… Why, I don`t know , just says it on the bottle. My problem is cat hairs, one of my cats uses the roof as a sun lounger. Anyone know a cat proofer for soft tops.
My white cat did the same. I hung an ultrasonic cat detterant on the fence next to where I park it, it works no more cat hair on the roof. Only downside is you have to remember to turn it off when you potter about on the car or you end up with a blinding headache!!
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Would that work from inside the car?
Having the water bead on the fabric is very satisfying. Has an MX5 roof ever become porous if left untreated though? I’ve had 14 so far (one for 10 years) and the only leaks came from worn out rubbers and stabbings. Never treated any of them.
Very worrying, stabbings? 
On the fabric “Mohair” soft top roof the rubber interlayer is very similiar to that used on EPDM roofing on houses and other flat roofing construction. This is currently estimated to have a life in excess of 50 years and most installers / manufacturers will have a warranty on such material of 25 to 30 years even in hot climates such as the Mid West states of the USA. Whilst soft tops are subject to additional stresses due to their very nature, unless they are subject to physical damage to this interlayer due to abrasion of either the Twill weave outer layer or the inner lining material suffering abrasion problems against interior objects ( ND?) then I would expect the material to be OK for a good time. Problems start when replacement hoods are poorly manufactured using blunt needles for the stitching or poor quality thread that does not properly seal the holes. Even one well known car manufaturer missed the blunt needle problem blaming the hood material for leaking along the stitching line when in fact they were using worn out needles of the wrong size and questionable thread, another “Cost Reduction” which went wrong.
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Yes, one of the present ones has a 3” stab in it that has been badly stitched up. Still doesn’t leak.