PU

What is PU-coated fabric?

PU stands for polyurethane. A PU-coated fabric consists of a textile base, usually polyester or nylon,
with a thin layer of polyurethane on one side. The construction is the same as for PVC, a textile base
plus a plastic coating, but the coating is thinner, softer and lighter.

Polyurethane is made from two main building blocks: an isocyanate and a polyol. The choice of
building blocks largely determines how the material behaves over time, which we come back to
below.

A dense PU coating does not let water through. With welded seams, PU garments are also fully
waterproof as long as the coating is intact. The coating does not let water vapour out either, so
condensation forms on the inside during exertion, just as in PVC. Breathable PU coatings do exist,
but they work like membranes and are covered under Breathable garments.

What PU does well

The main advantage is weight. A PU garment is light, supple and comfortable to move in, and it
packs down small. That makes the material practical for everyday wear, travel and shorter spells
outdoors.

PU stays soft in the cold better than conventional PVC. The difference narrows, however, compared
with modern PVC containing cold-resistant plasticisers.

Because the waterproofing lies in the coating itself rather than in a surface treatment, a PU garment,
like a PVC garment, needs no reproofing to keep water out.

Begränsningar att känna till

Den tunnare beläggningen tål mindre nötning. Vid hårt bruk slits den igenom snabbare, och knän, sittytor och axlar under bärremmar är typiska slitagepunkter.

Den förväntade livslängden är också kortare vid yrkesmässigt bruk. Det är ingen slump att kraftig PVC dominerar inom fiske och lantbruk medan PU dominerar i konsumentledet.

PU åldras genom hydrolys: fukt bryter långsamt ned polymeren, vilket kan göra att beläggningen med tiden blir klibbig, spricker eller flagnar, även på plagg som knappt använts men förvarats länge. Hur det går till förklarar vi i faktarutan nedan.

PU har sämre UV-beständighet i den vanligaste kemin. De flesta PU-beläggningar i konsumentplagg bygger på aromatiska polyuretaner (MDI- eller TDI-baserade), som fotooxiderar i solljus: polymeren gulnar och försprödas. Det syns tydligast på ljusa och genomskinliga plagg. Alifatiska polyuretaner gulnar inte på samma sätt, men de är dyrare, och UV-stabilisatorer kan bromsa förloppet i aromatiska system.

Färgäktheten är i praktiken svagare. En tunn PU-beläggning har lite material som kan bära pigment, och kulören sitter ofta i textilstommen eller i ett tunt toppskikt. När ytan nöts igenom eller gulnar syns det därför tydligt. I en tjockare PVC-beläggning blandas pigmentet i hela beläggningen, så färgen följer med när ytan slits.

Slutligen är PU svårare att reparera hållbart, eftersom tunna beläggningar ger ett lagningslim eller en lapp mindre material att fästa i.

Limitations worth knowing

The thinner coating withstands less abrasion. Under hard use it wears through faster, and the knees,
seat and shoulders under straps are typical wear points.

The expected service life is also shorter in professional use. It is no coincidence that heavy-duty PVC
dominates in fishing and farming, while PU dominates the consumer market.

PU ages through hydrolysis: moisture slowly breaks the polymer down, which over time can make
the coating sticky, cracked or flaking, even on garments that have hardly been used but have been
stored for a long time. We explain how this happens in the fact box below.
PU has poorer UV resistance in its most common chemistry. Most PU coatings in consumer garments
are based on aromatic polyurethanes (MDI- or TDI-based), which photo-oxidise in sunlight: the
polymer yellows and becomes brittle. This is most visible on light-coloured and transparent
garments. Aliphatic polyurethanes do not yellow in the same way, but they are more expensive, and
UV stabilisers can slow the process in aromatic systems.

Colourfastness is weaker in practice. A thin PU coating has little material to carry pigment, and the
colour often sits in the textile base or in a thin top layer. When the surface wears through or yellows,
this becomes clearly visible. In a thicker PVC coating, the pigment is mixed throughout the coating,
so the colour remains as the surface wears.

Finally, PU is harder to repair durably, because thin coatings give repair adhesive or a patch less
material to bond to.

Fact box: Hydrolysis – the mechanism behind PU ageing

The vast majority of PU coatings in consumer rainwear are based on a polyester polyol, which is
cheaper and more common in production than the more resistant polyether-based variant.
Polyester-based PU contains ester bonds in the polymer chain itself, and ester bonds are
precisely what water molecules can break through hydrolysis. Polyether-based PU lacks this
vulnerability and resists moisture considerably better, but it is more expensive, uncommon in
the budget segment and more sensitive to oxidation instead.

The breakdown happens in two stages. First, the weaker bonds between the urethane groups in
the polymer’s hard segments are broken. Then the ester bonds in the soft, flexible segment are
attacked. Every broken bond shortens the polymer chain, known as chain scission, and the
shorter the chains become, the more the material’s properties change.

Water is not just a trigger but a direct reactant. Without moisture there is no hydrolysis. Heat
speeds up the reaction considerably. A tent manufacturer that tests its PU-coated fabrics in a
climate chamber at around 70 °C and 95 % relative humidity, a so-called jungle test, reports that
one week of exposure corresponds to roughly one year of normal use. How quickly this happens
in practice varies widely: from a couple of years for cheap, unstabilised polyester PU in a warm,
humid climate, to decades for garments stored somewhere cool, dry and airy.

The coating becomes sticky because its molecular weight drops as the polymer chains are
cleaved, and shorter degradation fragments migrate to the surface.

Sometimes there is a smell as well. A known degradation product of ester cleavage is butyric
acid, which has a distinctive sour odour, often described as sour milk. The smell is an early,
practical sign that hydrolysis has started, independently described by several sources that work
with older PU-coated equipment.

The same chain scission that makes the material sticky eventually makes it brittle too. Cracking
is a sign of increased brittleness throughout the coating, and flaking means the coating cracks
and loses its adhesion to the fabric underneath. It gets worse the more flexible the base fabric
is, because movement stresses an already weakened coating. Both are end stages of the same
process that begins with stickiness.

PVC does not age in this way. Plasticised PVC lacks these ester bonds in its main chain and
degrades through entirely different mechanisms instead, such as dehydrochlorination under
heat and UV light, and plasticiser migration. Water is not a direct reactant in the same way. That
is why PVC-coated garments do not turn sticky from being stored in a damp wardrobe, whereas
PU garments can.

When does PU make sense?

PU is a good choice for light everyday use where low weight matters most: walks, commuting, travel and short spells in the rain. If you are out for long periods, are hard on your clothes or want a garment to last for decades, a heavier PVC-based fabric with modern plasticisers is the more durable choice. Read more under PVC – waterproof, hard-wearing rainwear.

If you choose PU, how you handle the garment can extend its life. Since hydrolysis is driven by moisture and heat, it is wise to always let the garment dry completely before putting it away, to store it somewhere cool, dry and airy rather than in a warm attic or a sealed bag, and not to leave it hanging in direct sunlight unnecessarily.

Lätt utan PU: Raintex Light+

Värt att veta för den som väljer PU främst för viktens skull: Farmerrains Raintex Light+ väger 250 g/m² och ligger därmed i samma viktklass som de kraftigare tygerna i PU-segmentet, men med en vinylbeläggning som inte gulnar av UV på det sätt PU gör och som inte åldras genom hydrolys. Mjukgöraren är den ftalatfria Pevalen™ Pro 100, och materialet är fritt från PFAS. PVC-belagd väv med UV-stabilisatorer och pigment används utomhus i årtionden, till exempel i markiser och tältdukar.

Låg vikt behöver alltså inte betyda PU:s åldringsegenskaper. Raintex Light+ är fortfarande ett tätt material som inte andas, så ventilation och val av underställ spelar samma roll som i andra regnkläder i galon.

Var tillverkas PU-plaggen?

Merparten av de PU-belagda konsumentregnkläder som säljs i Europa tillverkas i Asien, i linje med klädimporten i stort, eftersom EU:s konfektionsimport domineras av asiatiska producentländer. Det är i sig inte ett kvalitetsomdöme: bra plagg tillverkas på många platser. Men avståndet får tre konkreta konsekvenser som konsumenten sällan ser.

Den första är längre transporter mellan fabrik och marknad, med motsvarande klimatpåverkan. Den andra är svårare spårbarhet: ju fler mellanled, desto svårare att veta var väv, beläggning och kemikalier faktiskt kommer ifrån. Den tredje är att kemikaliekontrollen vilar på importören. REACH gäller varor som säljs i EU oavsett tillverkningsland, men efterlevnaden bygger på att importören verifierar innehållet, och EU:s varningssystem Safety Gate rapporterar återkommande fynd av begränsade ftalater i importerade plastvaror.

Slutsatsen är inte att tillverkningsland avgör kvalitet, utan att transparens gör det. Fråga alltid var ett plagg är tillverkat och vad beläggningen innehåller. En seriös tillverkare svarar på båda, oavsett kontinent.