{"id":7976,"date":"2025-12-23T09:00:00","date_gmt":"2025-12-23T09:00:00","guid":{"rendered":"https:\/\/uplastech.com\/co-extruded-weather-seal\/"},"modified":"2025-12-23T09:00:00","modified_gmt":"2025-12-23T09:00:00","slug":"co-extruded-weather-seal","status":"publish","type":"post","link":"https:\/\/uplastech.com\/ru\/co-extruded-weather-seal\/","title":{"rendered":"Coextruded Weather Seals: Soft Lip on a Rigid Base"},"content":{"rendered":"<style>\n.upl-blog{font-size:17px;line-height:1.78;color:#1f2937}\n.upl-blog p{margin:0 0 18px}\n.upl-blog h2{font-size:26px;line-height:1.3;color:#0b2b33;margin:46px 0 14px;font-weight:700;letter-spacing:-.015em}\n.upl-blog h3{font-size:19.5px;color:#0d3b47;margin:28px 0 10px;font-weight:700}\n.upl-blog ul,.upl-blog ol{margin:0 0 20px;padding-left:22px}\n.upl-blog li{margin:0 0 9px}\n.upl-blog figure{margin:0 0 34px}\n.upl-blog figure img{width:100%;height:auto;display:block;border-radius:10px}\n.upl-blog figcaption{font-size:13px;color:#6b7280;margin-top:10px;line-height:1.5}\n.upl-blog .toc{background:none;border:0;border-radius:0;padding:0;margin:0 0 34px}\n.upl-blog .toc .lwptoc{margin:0}\n.upl-blog .toc h4{margin:0 0 10px;font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#0d5563}\n.upl-blog .toc ol{margin:0;padding-left:18px;font-size:14.5px}\n.upl-blog .toc li{margin-bottom:6px}\n.upl-blog table{width:100%;border-collapse:collapse;font-size:14.5px;margin:0 0 10px}\n.upl-blog th{background:#0d3b47;color:#fff;text-align:left;padding:11px 13px;font-weight:600;font-size:13.5px;border:0}\n.upl-blog td{padding:11px 13px;border:0;border-bottom:1px solid #e8ebed;vertical-align:top}\n.upl-blog tbody tr:nth-child(even){background:#fafbfc}\n.upl-blog .tablecap{font-size:12.5px;color:#6b7280;margin:0 0 30px}\n.upl-blog .myth{background:#fff8ef;border:1px solid #f6ddbd;border-radius:8px;padding:16px 20px;margin:0 0 26px;font-size:15.5px}\n.upl-blog .myth b{color:#a85c10}\n.upl-blog .callout{background:#f2f8f9;border-radius:8px;padding:18px 22px;margin:0 0 26px;font-size:15.5px;border-left:3px solid #14707f}\n.upl-blog .faq h3{border-top:1px solid #eceff1;padding-top:22px;margin-top:0;font-size:18px}\n.upl-blog .faq h3:first-of-type{border-top:0;padding-top:0}\n.upl-blog .cta{background:linear-gradient(135deg,#0b2b33,#0d5563);color:#fff;border-radius:12px;padding:34px;margin:48px 0 30px}\n.upl-blog .cta h2,.upl-blog .cta .cta-h{color:#fff;margin:0 0 10px;font-size:24px;font-weight:700;line-height:1.3}\n.upl-blog .cta p{color:#c9dee3;margin:0 0 20px;font-size:16px}\n.upl-blog .btn{display:inline-block;background:#e07a1f;color:#fff;text-decoration:none;font-weight:700;padding:13px 26px;border-radius:8px;font-size:15.5px}\n.upl-blog .rel{border-top:1px solid #e8ebed;margin-top:40px;padding-top:26px}\n.upl-blog .rel h4{font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#6b7280;margin:0 0 14px}\n.upl-blog .rel ul{list-style:none;padding:0;margin:0}\n.upl-blog .rel li{padding:11px 0;border-bottom:1px dashed #e8ebed}\n.upl-blog .rel a{text-decoration:none;font-weight:600;font-size:15.5px}\n@media(max-width:640px){.upl-blog h2{font-size:22px}.upl-blog table{font-size:13px}.upl-blog .cta{padding:24px}}\n\/* \u5355\u7bc7\u9875\u9690\u85cf WhatsApp \u95ee\u5019\u5361\uff0c\u53ea\u4fdd\u7559\u5706\u5f62\u6c14\u6ce1\uff0c\u907f\u514d\u906e\u6321\u4fa7\u680f\u8be2\u76d8\u63d0\u4ea4\u6309\u94ae\u3002\n   \u6ce8\u610f\uff1aClick to Chat \u7684\u70b9\u51fb\u903b\u8f91\u662f\u300c\u95ee\u5019\u5361\u5143\u7d20\u5b58\u5728\u5c31\u4e0d\u8df3\u8f6c\u300d\uff0c\u53ea\u9760 CSS \u9690\u85cf\u4f1a\u8ba9\u6c14\u6ce1\u53d8\u6210\u6b7b\u94fe\u63a5\u3002\n   Code Snippets #9\u300cUPL single post: WhatsApp bubble jumps straight to chat\u300d\u8d1f\u8d23\u628a\u8be5\u8282\u70b9\u4ece DOM \u79fb\u9664\uff0c\n   \u4e0b\u9762\u8fd9\u6761 CSS \u53ea\u662f\u79fb\u9664\u524d\u7684\u89c6\u89c9\u515c\u5e95\u3002\u5220 #9 \u524d\u5fc5\u987b\u5148\u5220\u8fd9\u6761\u89c4\u5219\u3002 *\/\nbody.single-post .ht_ctc_chat_greetings_box{display:none !important}\n<\/style>\n<div class=\"upl-blog\">\n<figure>\n<img fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/10\/co-extruded-weather-seal.jpg\" alt=\"Water penetration pressure against seal compression, and sealing force retained against ageing time\" width=\"1536\" height=\"909\"><figcaption>Penetration pressure reaches 900 Pa at 50 percent compression but gains halve past 30, while 2000 hours at 70 C costs 36 percent of the sealing force.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"job\">What a weather seal has to stop<\/h2>\n<p>A weather seal on a window or a door has to stop three things: water driven by wind, air leakage, and noise. Water is the hardest, because it arrives with pressure behind it and because it will find any path that is not blocked.<\/p>\n<p>The seal is only one part of the system. A window that leaks usually has a seal that is compressed too little, a drainage path that is blocked, or a corner that is not sealed at all. The profile is the visible component, and it is rarely the only cause.<\/p>\n<p>The coextruded construction exists because the two jobs are different. The rigid base holds the seal in the frame and keeps the profile straight over a two metre length; the soft lip deflects against the sash and takes up the tolerance in the frame. A single material cannot do both.<\/p>\n<h2 id=\"water\">Compression buys watertightness, then stops<\/h2>\n<p>Water penetration pressure rises with seal compression, and the relationship has a clear knee. At 10 percent compression the seal holds about 150 Pa, at 20 percent 350, at 30 percent 600, at 40 percent 800 and at 50 percent 900.<\/p>\n<p>The gain per ten percent of compression is 200 Pa from 10 to 20, 250 from 20 to 30, then 200 and 100. Past 30 percent the seal is already in contact along its whole length and further compression only increases the contact stress; it does not close any new path.<\/p>\n<p>This matters because compression is not free. A seal compressed to 50 percent needs a frame stiff enough to take the reaction force, and a sash that can be closed against it. The usual design target is 25 to 35 percent compression, which gives 500 to 700 Pa of water resistance with a closing force a person can manage.<\/p>\n<table>\n<thead>\n<tr>\n<th>Compression<\/th>\n<th>Penetration pressure<\/th>\n<th>Gain per 10 points<\/th>\n<th>Note<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>10 percent<\/td>\n<td>150 Pa<\/td>\n<td>n\/a<\/td>\n<td>Intermittent contact, leaks at corners<\/td>\n<\/tr>\n<tr>\n<td>20 percent<\/td>\n<td>350 Pa<\/td>\n<td>200 Pa<\/td>\n<td>Light rain only<\/td>\n<\/tr>\n<tr>\n<td>30 percent<\/td>\n<td>600 Pa<\/td>\n<td>250 Pa<\/td>\n<td>The usual design point<\/td>\n<\/tr>\n<tr>\n<td>40 percent<\/td>\n<td>800 Pa<\/td>\n<td>200 Pa<\/td>\n<td>Driving rain, higher closing force<\/td>\n<\/tr>\n<tr>\n<td>50 percent<\/td>\n<td>900 Pa<\/td>\n<td>100 Pa<\/td>\n<td>Diminishing returns<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Water penetration pressure against seal compression, on a coextruded EPDM lip.<\/p>\n<h2 id=\"ageing\">Ageing is what opens it<\/h2>\n<p>A new seal passes the water test. The one that leaks is three years old, and it leaks because the lip has lost its recovery. Accelerated ageing at 70 C takes the sealing force from 100 percent to 92 after 250 hours, 85 after 500, 76 after 1000 and 64 after 2000.<\/p>\n<p>A 36 percent loss of force is a 36 percent loss of contact stress, and the compression that was 30 percent when new is effectively 19 percent three years later. That is below the knee in Table 1, which is why an old window leaks in weather it used to keep out.<\/p>\n<p>The material decides the rate. An EPDM lip holds its recovery better than a standard TPE at the same temperature, and a silicone lip better still, at a higher cost. The specification should quote the retained force after ageing at the service temperature, not the initial hardness.<\/p>\n<div class=\"callout\">Specify retained sealing force after 1000 hours at the service temperature. A seal that passes on day one and fails at year three has passed the wrong test.<\/div>\n<h2 id=\"drainage\">Drainage and pressure equalisation<\/h2>\n<p>A weather seal is not a waterproof barrier on its own. The principle that makes a window watertight is the same one that makes a roof work: the outer seal slows the water, an internal drainage chamber carries it away, and a second seal stops the air.<\/p>\n<p>That is why the profile has chambers and why the frame has drain slots. Water that gets past the outer lip runs down the chamber and out through a slot at the bottom, rather than being forced further in by the pressure difference. A frame with blocked drain slots will leak whatever the seal does.<\/p>\n<p>Pressure equalisation matters as much. If the chamber between the two seals is at a different pressure from the outside, water is pushed or drawn across the inner seal. A small vent to the outside equalises the pressure and removes the driving force, and it costs nothing but a hole that has to be designed in.<\/p>\n<h2 id=\"corners\">Corners are where it leaks<\/h2>\n<p>A straight run of seal compresses evenly and leaks rarely. The corners are where the profile has to change direction, and there are only three ways to do it: a moulded corner, a mitred and welded corner, or a cut and butted corner.<\/p>\n<p>A cut and butted corner is the cheapest and the worst. The two ends do not meet exactly, the compression at the joint is lower than along the run, and the joint opens as the frame moves. A welded mitre is better if the weld is complete; a moulded corner is best, because the material is continuous through the change of direction.<\/p>\n<p>The corner is also where the seal meets the hardware. A hinge or a lock case interrupts the seal line, and the interruption has to be covered by a gasket or a shaped block. A window that leaks at the bottom corners almost always has an interruption there that nobody detailed.<\/p>\n<table>\n<thead>\n<tr>\n<th>Corner type<\/th>\n<th>Compression at joint<\/th>\n<th>\u0421\u0442\u043e\u0438\u043c\u043e\u0441\u0442\u044c<\/th>\n<th>Where it is used<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Cut and butted<\/td>\n<td>Low, uneven<\/td>\n<td>Lowest<\/td>\n<td>Cheap frames, and it shows<\/td>\n<\/tr>\n<tr>\n<td>Mitred and welded<\/td>\n<td>Good if the weld is complete<\/td>\n<td>\u0421\u0440\u0435\u0434\u043d\u0438\u0439<\/td>\n<td>Standard commercial<\/td>\n<\/tr>\n<tr>\n<td>Moulded corner<\/td>\n<td>\u041d\u0435\u043f\u0440\u0435\u0440\u044b\u0432\u043d\u044b\u0439<\/td>\n<td>Highest<\/td>\n<td>High-performance and passive house<\/td>\n<\/tr>\n<tr>\n<td>Corner block with gasket<\/td>\n<td>\u0425\u043e\u0440\u043e\u0448\u043e<\/td>\n<td>\u0421\u0440\u0435\u0434\u043d\u0438\u0439<\/td>\n<td>Where hardware interrupts the line<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Corner details and how each one behaves under compression.<\/p>\n<h2 id=\"specify\">What to specify<\/h2>\n<p>A weather seal specification that only quotes hardness and colour will be filled with whatever is on the line. Six lines make it a specification.<\/p>\n<ul>\n<li>Compression range at the installed gap, with the closing force it implies.<\/li>\n<li>Water penetration pressure at the design compression, to the test standard used.<\/li>\n<li>Retained sealing force after 1000 hours at the service temperature.<\/li>\n<li>Corner detail: moulded, welded or butted, and the joint compression.<\/li>\n<li>Drainage and venting: slot positions and the pressure equalisation path.<\/li>\n<li>Material of the lip and of the base, quoted separately.<\/li>\n<\/ul>\n<p>The retained force is the one to hold firm on, because it is the only number that predicts how the window behaves in year three rather than on the day it was installed.<\/p>\n<div class=\"faq\">\n<h3>How much should a weather seal be compressed?<\/h3>\n<p>25 to 35 percent of its free height. That gives 500 to 700 Pa of water penetration resistance, and gains halve past 30 percent while the closing force keeps rising.<\/p>\n<h3>Why does an old window leak when it did not before?<\/h3>\n<p>The seal has lost recovery. Ageing at 70 C costs about 36 percent of the sealing force in 2000 hours, so a 30 percent compression becomes an effective 19 percent.<\/p>\n<h3>What is the best corner detail for a weather seal?<\/h3>\n<p>A moulded corner, because the material is continuous through the change of direction. A welded mitre is next; a cut and butted corner leaks first.<\/p>\n<h3>Do weather seals need drainage?<\/h3>\n<p>Yes. The seal slows the water, a drainage chamber carries it out through slots, and a second seal stops the air. A blocked drain slot will leak whatever the seal does.<\/p>\n<h3>What is pressure equalisation in a window frame?<\/h3>\n<p>A small vent between the outer and inner seals so the chamber is at outside pressure. Without it, the pressure difference pushes water across the inner seal.<\/p>\n<h3>EPDM or TPE for a weather seal?<\/h3>\n<p>EPDM holds recovery better over time and at temperature. TPE is cheaper, bonds more easily to a rigid carrier, and is adequate for internal or mild climates.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Specifying a weather seal for a window or door system?<\/p>\n<p>Send the frame gap, the service temperature and the water test you have to pass. We will come back with a compression range, a corner detail and a retained force figure.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/ru\/%d0%bf%d0%b2%d1%85-%d0%bf%d1%80%d0%be%d1%84%d0%b8%d0%bb%d0%b8\/\">Talk to a profile engineer<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/ru\/seal-strip-profile\/\">Seal Strip Profiles: Flexible and Rigid in One Extrusion<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/door-profile-design\/\">Door Profile Design: Chambers, Thresholds and Weather Seals<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/window-profile-reinforcement\/\">Window Profile Reinforcement: Steel, Fibre or Nothing<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/aluminium-replacement-profile\/\">Aluminium Replacement Profiles: Where PVC Wins and Where It Does Not<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/%d0%bf%d0%b2%d1%85-%d0%bf%d1%80%d0%be%d1%84%d0%b8%d0%bb%d0%b8\/\">PVC Profiles: Extrusion, Tooling and Tolerances<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Water penetration pressure climbs from 150 Pa at 10 percent compression to 900 at 50, but halves its rate past 30. Ageing at 70 C takes a third of the sealing force in 2000 hours, and that is what opens the gap.<\/p>","protected":false},"author":1,"featured_media":7975,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-7976","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-plastic-extrusion-process"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/posts\/7976","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/comments?post=7976"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/posts\/7976\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/media\/7975"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/media?parent=7976"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/categories?post=7976"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/tags?post=7976"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}