{"id":8017,"date":"2026-01-12T09:00:00","date_gmt":"2026-01-12T09:00:00","guid":{"rendered":"https:\/\/uplastech.com\/pvc-foam-board-extrusion\/"},"modified":"2026-01-12T09:00:00","modified_gmt":"2026-01-12T09:00:00","slug":"pvc-foam-board-extrusion","status":"publish","type":"post","link":"https:\/\/uplastech.com\/ja\/pvc-foam-board-extrusion\/","title":{"rendered":"PVC Foam Board: The Lightest Sheet Is the Worst Insulator"},"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\/pvc-foam-board-extrusion.jpg\" alt=\"Board density against blowing agent level, and thermal conductivity against board density\" width=\"1536\" height=\"909\"><figcaption>Density falls from 0.75 to 0.42 g\/cm3 across the dose range, while conductivity has a minimum of 0.035 W\/mK at 0.45 g\/cm3.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"notmaterial\">Foam board is a density specification, not a material<\/h2>\n<p>Two boards with the same formulation and the same thickness can differ by a factor of two in weight, strength and insulation, and the difference is the density. That is why a foam board drawing that specifies only the material and the thickness is not a specification. The density is the product.<\/p>\n<p>Density is set by the amount of gas that stays in the sheet, and the gas comes from a chemical blowing agent that decomposes in the barrel. More agent means more gas, more expansion and lower density. The relationship is monotonic and it is not linear, because the last of the gas has to expand against a melt that is already full of cells.<\/p>\n<p>Everything downstream follows from that one number. Strength falls roughly with the square of density, stiffness with the cube, and thermal conductivity has a minimum in the middle of the range rather than at either end. Choosing a density is choosing a position on three curves at once.<\/p>\n<h2 id=\"dose\">Each 0.2 phr buys less than the last<\/h2>\n<p>Measured across a typical azodicarbonamide dose range, 0.4 phr gives 0.75 g\/cm3, 0.6 gives 0.62, 0.8 gives 0.52, 1.0 gives 0.45 and 1.2 gives 0.42. The first 0.2 phr removes 0.13 g\/cm3. The last 0.2 phr removes 0.03. The return falls by a factor of four across the range.<\/p>\n<p>The reason is that gas yield saturates while cell coalescence accelerates. Once the melt has expanded to the point where the cell walls are thin, additional gas does not create new cells, it inflates existing ones until neighbouring cells merge. Coalesced cells are larger, weaker and worse insulators, and they are the beginning of the surface defects that make a board unsaleable.<\/p>\n<p>This is the argument against specifying the lowest density a supplier can quote. A board at 0.42 g\/cm3 is not a better version of a board at 0.52. It is a board with fewer, larger cells, a rougher surface after sanding, and a much narrower processing window, because the margin between full expansion and collapse has been spent.<\/p>\n<h2 id=\"lambda\">The lightest board is the worst insulator<\/h2>\n<p>Thermal conductivity in a foam has three contributions: conduction through the polymer, conduction through the gas in the cells, and radiation across the cell walls. Density changes all three in opposite directions, and the sum has a minimum.<\/p>\n<p>At high density there is simply more polymer per unit volume, and polymer conducts about twenty times better than the gas it replaces, so conductivity rises. At low density the cell walls become thin and the cells become large, radiation passes across them more freely, and conductivity rises again. The measured curve runs 0.038 at 0.40 g\/cm3, 0.035 at 0.45, 0.036 at 0.52, 0.039 at 0.62 and 0.045 at 0.75.<\/p>\n<p>The minimum at 0.45 is the density at which the two penalties cross. Below it, the board is lighter, weaker and a worse insulator. That combination is why a specification written as a maximum density is a specification that will produce a worse product at the same price.<\/p>\n<p>The practical consequence for a wall or a panel is that insulation per kilogram has an optimum too, and it sits above the minimum-density point, because a thicker board of slightly higher density outperforms a thin board of the lowest density at the same weight.<\/p>\n<h2 id=\"screw\">What the screw has to do, and where it fails<\/h2>\n<p>The blowing agent decomposes under temperature and pressure, and the gas has to stay dissolved in the melt until the die. That is a pressure job, and it is the part of foam extrusion that a general-purpose screw gets wrong.<\/p>\n<table>\n<thead>\n<tr>\n<th>Screw zone<\/th>\n<th>Job<\/th>\n<th>What goes wrong<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Feed<\/td>\n<td>Convey and compact without premature heating<\/td>\n<td>Agent decomposes early, gas escapes at the hopper<\/td>\n<\/tr>\n<tr>\n<td>Compression<\/td>\n<td>Melt and seal, build pressure<\/td>\n<td>Pressure too low, gas comes out of solution as large bubbles<\/td>\n<\/tr>\n<tr>\n<td>Metering<\/td>\n<td>Homogenise temperature and gas concentration<\/td>\n<td>Temperature variation becomes density variation along the board<\/td>\n<\/tr>\n<tr>\n<td>Decompression<\/td>\n<td>Drop pressure just before the die<\/td>\n<td>Too much drop, premature foaming inside the adapter<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 The four zones and the foam-specific failure in each<\/p>\n<p>The most common failure is not the screw at all, it is the temperature profile. A flat profile heats the feed zone too much, and the agent starts decomposing before the polymer has melted enough to hold the gas. The result is a board with a coarse, irregular cell structure and a density that wanders along the length, which the operator then tries to fix by adding more agent.<\/p>\n<p>A rising profile, cool at the feed and hot at the die, keeps the agent intact until there is enough pressure and enough melt to dissolve the gas. It costs nothing and it is the single largest lever on cell uniformity.<\/p>\n<h2 id=\"cells\">Cell structure is what the customer actually sees<\/h2>\n<p>A foam board has a skin, and the skin is not foam. It forms where the melt touches the die and the calibrator, it is solid, and its thickness sets the surface finish. A board with a 0.3 mm skin sands and prints well. A board with a 0.05 mm skin shows the cells underneath as a mottled surface the moment anyone touches it with abrasive.<\/p>\n<p>Cell size matters more than cell count for machining. A board with 0.3 mm cells cuts cleanly and takes a screw. A board with 1 mm cells tears out around a drill and crumbles at an edge. The difference is not visible on the surface, so it has to be specified and checked on a cut section.<\/p>\n<table>\n<thead>\n<tr>\n<th>\u6b20\u9665<\/th>\n<th>\u539f\u56e0<\/th>\n<th>Fix<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Coarse cells in the core<\/td>\n<td>Gas released before full melt<\/td>\n<td>Cooler feed zone, higher back pressure<\/td>\n<\/tr>\n<tr>\n<td>Density varies along the board<\/td>\n<td>Temperature drift in metering<\/td>\n<td>Stabilise the profile, check the heater bands<\/td>\n<\/tr>\n<tr>\n<td>Rough surface after sanding<\/td>\n<td>Skin too thin<\/td>\n<td>Lower die temperature, raise calibrator cooling<\/td>\n<\/tr>\n<tr>\n<td>Collapsed cells, wavy surface<\/td>\n<td>Too much agent, cells merge<\/td>\n<td>Reduce dose, accept higher density<\/td>\n<\/tr>\n<tr>\n<td>Thick skin, heavy board<\/td>\n<td>Die too cold or calibrator over-cooled<\/td>\n<td>Raise die temperature slightly<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Foam board defects and the setting that removes each<\/p>\n<h2 id=\"specify\">What to specify<\/h2>\n<p>A foam board specification needs five numbers, and density is only one of them.<\/p>\n<ul>\n<li>Density, with a tolerance, as a target rather than a maximum.<\/li>\n<li>Cell size on a cut section, not on the surface.<\/li>\n<li>Skin thickness, if the board will be sanded, printed or bonded.<\/li>\n<li>Thermal conductivity at the specified density, because it is not monotonic.<\/li>\n<li>Dimensional tolerance and flatness, which depend on cooling and on the density gradient through the thickness.<\/li>\n<\/ul>\n<p>If the board is going into a structural application, add the compressive strength at 10 percent deflection. It falls with the square of density, so a 10 percent density reduction costs about 19 percent of the strength, and that is usually the number that decides whether the panel passes.<\/p>\n<div class=\"myth\">Myth: lower density means a cheaper board. Resin cost per cubic metre does fall, but insulation per millimetre falls faster below 0.45 g\/cm3, so the thickness needed for a given U-value goes up and the installed cost can rise. The cheapest wall is rarely the lightest board.<\/div>\n<div class=\"faq\">\n<h3>What density should a PVC foam board be?<\/h3>\n<p>0.45 to 0.55 g\/cm3 for most signage and furniture panels. Below 0.45 the insulation and the machining quality both fall.<\/p>\n<h3>Why does thermal conductivity rise again at low density?<\/h3>\n<p>Cells get larger and walls get thinner, so radiation crosses them more freely. Conduction through polymer falls, radiation rises, and the sum has a minimum.<\/p>\n<h3>How much blowing agent does a foam board need?<\/h3>\n<p>0.6 to 1.0 phr of azodicarbonamide for the 0.45 to 0.62 g\/cm3 range. Above 1.0 phr the return falls and cell coalescence starts.<\/p>\n<h3>Why does density vary along the board?<\/h3>\n<p>Usually a temperature drift in the metering zone, which changes how much gas stays in solution. Check the heater bands before changing the formulation.<\/p>\n<h3>What causes a rough surface after sanding?<\/h3>\n<p>A skin that is too thin. The cells underneath are exposed, and no amount of sanding makes them smooth.<\/p>\n<h3>Does lower density mean lower cost?<\/h3>\n<p>Not necessarily. Insulation per millimetre falls below 0.45 g\/cm3, so more thickness is needed for the same performance and the installed cost can rise.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">A foam board that has to hold a tolerance?<\/p>\n<p>Send the density target, the thickness and what the board has to do. We will tell you where it sits on the conductivity curve and whether the cell structure will machine.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/ja\/%e3%83%9d%e3%83%aa%e5%a1%a9%e5%8c%96%e3%83%93%e3%83%8b%e3%83%bc%e3%83%ab%e3%81%ae%e6%b3%a1%e3%81%ae%e6%94%be%e5%87%ba\/\">Ask about PVC foam extrusion<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/ja\/%e3%83%9d%e3%83%aa%e5%a1%a9%e5%8c%96%e3%83%93%e3%83%8b%e3%83%bc%e3%83%ab%e3%83%97%e3%83%ad%e3%83%95%e3%82%a1%e3%82%a4%e3%83%ab\/\">PVC Profiles: Extrusion, Tolerance and Finish<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ja\/pet-sheet-extrusion\/\">PET Sheet Extrusion: Crystallinity, IV Drop and Grade<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ja\/profile-cnc-fabrication\/\">Profile CNC Fabrication: Cutting Without Changing the Face<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ja\/decking-profile-extrusion\/\">Decking Profile Extrusion: Grip, Gap and Movement<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ja\/co-extruded-weather-seal\/\">Co-extruded Weather Seal: When Two Materials Must Match<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Density falls from 0.75 to 0.42 g\/cm3 as blowing agent goes from 0.4 to 1.2 phr, and each 0.2 phr buys less than the one before. Thermal conductivity bottoms out at 0.45 g\/cm3, so the lightest board is not the best insulator and not the cheapest wall.<\/p>","protected":false},"author":1,"featured_media":8016,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-8017","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\/ja\/wp-json\/wp\/v2\/posts\/8017","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/ja\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/ja\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ja\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ja\/wp-json\/wp\/v2\/comments?post=8017"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/ja\/wp-json\/wp\/v2\/posts\/8017\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ja\/wp-json\/wp\/v2\/media\/8016"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/ja\/wp-json\/wp\/v2\/media?parent=8017"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/ja\/wp-json\/wp\/v2\/categories?post=8017"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/ja\/wp-json\/wp\/v2\/tags?post=8017"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}