{"id":7946,"date":"2025-12-08T09:00:00","date_gmt":"2025-12-08T09:00:00","guid":{"rendered":"https:\/\/uplastech.com\/thermoforming-drape-forming\/"},"modified":"2025-12-08T09:00:00","modified_gmt":"2025-12-08T09:00:00","slug":"thermoforming-drape-forming","status":"publish","type":"post","link":"https:\/\/uplastech.com\/id\/thermoforming-drape-forming\/","title":{"rendered":"Drape Forming: The Oldest Method and Where It Still Wins"},"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\/thermoforming-drape-forming.jpg\" alt=\"Wall thickness ratio against draw ratio for drape and vacuum forming, and tooling cost index by method\" width=\"1536\" height=\"909\"><figcaption>Drape holds a 0.70 wall ratio at a 0.2 draw against 0.62 for vacuum, on a tooling cost index of 1.0 against 1.3.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"method\">Drape forming in one sentence<\/h2>\n<p>Heat a sheet, lift it, drop it over a male mould, and let gravity and a little mechanical assist pull it down. That is the whole process. There is no vacuum pump, no pressure box, no female cavity and no air-tight seal, which is why it is the oldest thermoforming method and why it is still in use.<\/p>\n<p>The sheet is clamped in a frame and heated from above to its forming temperature, typically 150 to 170 C for acrylic and 140 to 160 C for ABS. The frame then descends over the mould, or the mould rises into the sheet, and the material drapes. A top plate or a ring can press the sheet against the mould to sharpen the edges, but the forming force is gravity plus whatever the operator adds.<\/p>\n<p>Because there is no pressure difference, there are no vacuum holes. That single fact is the reason drape forming survives: a vacuum hole leaves a mark on the part, and on a display panel, a light diffuser or a sign face, a mark is a reject.<\/p>\n<h2 id=\"wall\">Why the wall holds better<\/h2>\n<p>Counter-intuitively, a process with less force gives a more even wall in shallow draws. The reason is that the sheet is stretched over the mould progressively from the contact point outward, and the material that has already touched the tool stops stretching because friction and cooling lock it. The rest of the sheet is drawn from the unformed area, which is still hot and still thick.<\/p>\n<p>At a draw ratio of 0.2, the ratio of depth to width, drape forming gives a thinnest-to-thickest wall ratio of about 0.70 against 0.62 for vacuum. At 0.6 it is 0.55 against 0.44, and at 1.0 it is 0.42 against 0.30. Drape is better at every depth, and the gap widens as the draw gets deeper.<\/p>\n<p>Vacuum does the opposite of what people expect because it pulls the sheet into contact everywhere at once. The sheet bridges the cavity, then snaps down, and the material that ends up in the corners has travelled from the middle of the sheet and thinned on the way. Drape never has that snap.<\/p>\n<table>\n<thead>\n<tr>\n<th>Draw ratio<\/th>\n<th>Drape wall ratio<\/th>\n<th>Vacuum wall ratio<\/th>\n<th>Difference<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>0.2<\/td>\n<td>0.70<\/td>\n<td>0.62<\/td>\n<td>+0.08<\/td>\n<\/tr>\n<tr>\n<td>0.4<\/td>\n<td>0.62<\/td>\n<td>0.52<\/td>\n<td>+0.10<\/td>\n<\/tr>\n<tr>\n<td>0.6<\/td>\n<td>0.55<\/td>\n<td>0.44<\/td>\n<td>+0.11<\/td>\n<\/tr>\n<tr>\n<td>0.8<\/td>\n<td>0.48<\/td>\n<td>0.36<\/td>\n<td>+0.12<\/td>\n<\/tr>\n<tr>\n<td>1.0<\/td>\n<td>0.42<\/td>\n<td>0.30<\/td>\n<td>+0.12<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Thinnest-to-thickest wall ratio by draw ratio, drape against vacuum.<\/p>\n<p>The wall ratio matters because it sets the design thickness. If the minimum wall has to be 1.2 mm and the ratio is 0.70, the sheet can be 1.7 mm. At a ratio of 0.44 the same minimum wall needs a 2.7 mm sheet, which is 60 percent more material and a longer heating cycle.<\/p>\n<h2 id=\"limits\">What it cannot do<\/h2>\n<p>The limits are all consequences of having no pressure. Drape forming cannot pull the sheet into a female cavity, so any feature on the outside of the part has to be a feature of the male mould, which means the outside surface is the one that touches the tool. On a display part you usually want the opposite: the visible face away from the tool, so that tool marks are on the hidden side.<\/p>\n<p>It cannot form a sharp internal corner. The sheet has to wrap around the mould, and the wrap radius is set by the sheet thickness and the material's stiffness, not by the mould radius. On a 3 mm acrylic sheet, a 3 mm mould radius produces a 5 to 6 mm outside radius because the material bridges the corner. Vacuum with a female tool can do better on the inside surface, because the sheet is pulled into the corner rather than wrapped around it.<\/p>\n<p>It cannot hold a deep draw without webbing. Beyond a draw ratio of about 1.0 the sheet folds as it descends, and the folds become permanent creases. A plug or a ring delays the onset but does not remove it. For deep parts, vacuum or pressure with a plug is the only route.<\/p>\n<div class=\"callout\">The honest summary: drape forming is for shallow, thick, single-curvature parts where the visible face must stay unmarked. Everything else belongs to a process with a pressure difference.<\/div>\n<h2 id=\"tooling\">One male mould, no vacuum system<\/h2>\n<p>The tooling cost index tells the story. Taking drape as 1.0, a vacuum tool is 1.3, a pressure box 1.6 and matched metal dies 4.0. The drape tool is cheaper for three reasons: it is male rather than female, it needs no vacuum circuit or seal, and it can be made from a material that would not survive a pressure load.<\/p>\n<p>For prototypes and short runs the mould is often medium-density fibreboard or a cast epoxy, sealed and sanded. For production it is aluminium, sometimes with a water circuit if the cycle is short. A 1 m by 2 m aluminium drape mould is a few thousand euros rather than the five figures a matched die set costs.<\/p>\n<table>\n<thead>\n<tr>\n<th>Metode<\/th>\n<th>Tooling cost index<\/th>\n<th>Mould type<\/th>\n<th>Vacuum system<\/th>\n<th>Typical volume<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Drape<\/td>\n<td>1.0<\/td>\n<td>Male, single surface<\/td>\n<td>None<\/td>\n<td>1 to 500 parts<\/td>\n<\/tr>\n<tr>\n<td>Vacuum<\/td>\n<td>1.3<\/td>\n<td>Female cavity<\/td>\n<td>Required<\/td>\n<td>100 to 10,000<\/td>\n<\/tr>\n<tr>\n<td>Pressure box<\/td>\n<td>1.6<\/td>\n<td>Female cavity, sealed<\/td>\n<td>Vacuum plus pressure<\/td>\n<td>500 to 50,000<\/td>\n<\/tr>\n<tr>\n<td>Matched metal<\/td>\n<td>4.0<\/td>\n<td>Male and female<\/td>\n<td>None<\/td>\n<td>10,000 and up<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Tooling cost and the equipment each method needs.<\/p>\n<p>The absence of a vacuum system also shortens the commissioning. There is no seal to leak, no vent to drill, no pump to size, and no leak test. A drape job can be set up on a machine with a heater and a clamp frame, which is why it is the method of choice for a workshop that forms one or two large parts a week.<\/p>\n<h2 id=\"wins\">Where it still wins<\/h2>\n<p>Signage is the classic case. A 5 mm acrylic sign face with a gentle curve, a folded return and a clean edge is a drape job, because the face has to be optically clear and any vacuum mark would be visible under a light. The same applies to light diffusers, where a mark becomes a bright spot.<\/p>\n<p>Sanitaryware and bathtub surrounds in thick acrylic are drape formed for a different reason: the sheet is 4 to 6 mm and the draw is shallow, so the wall ratio advantage is large and the material cost dominates. A 10 percent better wall ratio on a 5 mm sheet is 0.5 mm of acrylic across the whole part.<\/p>\n<p>Prototypes and architectural mock-ups are the third case. A single curved panel for a client approval does not justify a vacuum tool, and a drape mould can be made in a day from board and filler. It is also the fastest way to check whether a shape is formable at all before committing to a tool.<\/p>\n<h2 id=\"run\">Running a drape job<\/h2>\n<p>The process window is narrow in temperature and wide in everything else. Too cold and the sheet will not conform, leaving a bridge at the corner. Too hot and it sags before it reaches the mould, thinning the middle and marking the surface where it touches the heater frame.<\/p>\n<p>Heat the sheet evenly, and heat it from both sides if the machine allows. A single-sided heater on a 5 mm sheet gives a temperature gradient through the thickness that shows up as a difference in the radius on the two faces. Soak time matters more than heater power: acrylic needs to be at temperature through its thickness, not just at the surface.<\/p>\n<p>Drop the frame quickly and hold it. A slow descent lets the sheet cool in a partially formed shape, and the result is a part with a soft radius on one side and a sharp one on the other. Hold until the part is below the material's softening range, then release the clamp and let it cool on the mould if the mould can take it.<\/p>\n<p>The most common defect is not a wrinkle or a thin wall. It is a part that is right on the mould and wrong when it comes off, because the sheet was released while it was still above its heat deflection temperature and it sprang back. The fix is a longer hold, not a different mould.<\/p>\n<div class=\"faq\">\n<h3>What is drape forming?<\/h3>\n<p>Heating a thermoplastic sheet and letting it drape over a male mould under gravity, with no vacuum or pressure. It is the simplest thermoforming method and needs only a heater, a clamp frame and one mould.<\/p>\n<h3>Is drape forming better than vacuum forming?<\/h3>\n<p>For shallow draws it gives a more even wall, about 0.70 against 0.62 at a 0.2 draw ratio, and it leaves no vacuum marks. Vacuum is better for deep draws, female features and higher volume.<\/p>\n<h3>Why does drape forming leave no marks?<\/h3>\n<p>Because there are no vacuum holes. The forming force is gravity and the sheet is not pulled against a perforated surface, so the visible face stays clean.<\/p>\n<h3>What draw depth can drape forming reach?<\/h3>\n<p>About a 1.0 draw ratio, depth over width. Beyond that the sheet folds as it descends and the folds become permanent creases.<\/p>\n<h3>What materials are drape formed?<\/h3>\n<p>Thick acrylic is the most common, at 3 to 6 mm, along with ABS, polycarbonate and HIPS. The method suits materials that are stiff enough to hold their shape while hot.<\/p>\n<h3>How much does a drape mould cost?<\/h3>\n<p>About 1.0 on a tooling index where vacuum is 1.3 and matched metal is 4.0. Prototype moulds in board or cast epoxy are cheaper still.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Have a shallow, thick-walled part that keeps getting rejected?<\/p>\n<p>Send the drawing and the visible face. If the draw is under 1.0 and the part has to stay unmarked, drape forming is probably cheaper and better than the vacuum tool you were quoted.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/id\/custom-vacuum-forming\/\">Ask about drape forming<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/id\/thermoforming-vacuum-vs-pressure\/\">Vacuum Versus Pressure Forming: Detail, Cost and the Tool Each Needs<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/id\/thermoforming-pressure-box-forming\/\">Pressure Box Forming: What 500 kPa Buys You<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/id\/thermoforming-free-forming\/\">Free Forming: Shaping Without a Mould Surface<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/id\/pmma-acrylic-thermoforming\/\">PMMA Acrylic Thermoforming: Heat, Dry and Form<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/id\/custom-vacuum-forming\/\">Custom Vacuum Forming: Tooling, Materials and Tolerances<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Drape forming holds a 0.70 wall ratio at a 0.2 draw where vacuum gives 0.62, and it needs one male mould and no vacuum system. It also cannot form a sharp internal corner, and that limit is why it survives only in a few places.<\/p>","protected":false},"author":1,"featured_media":7945,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"Drape Forming: Wall Ratio, Tooling and Limits","_seopress_titles_desc":"Drape forming explained: wall uniformity against draw ratio compared with vacuum, tooling cost against pressure box and matched metal, why thick acrylic and sig","_seopress_robots_index":"","_seopress_robots_follow":"","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"29","_seopress_robots_breadcrumbs":"","_seopress_robots_freeze_modified_date":"","_seopress_robots_custom_modified_date":"","_seopress_robots_canonical":"","_seopress_social_fb_title":"","_seopress_social_fb_desc":"","_seopress_social_fb_img":"","_seopress_social_fb_img_attachment_id":0,"_seopress_social_fb_img_width":0,"_seopress_social_fb_img_height":0,"_seopress_social_twitter_title":"","_seopress_social_twitter_desc":"","_seopress_social_twitter_img":"","_seopress_social_twitter_img_attachment_id":0,"_seopress_social_twitter_img_width":0,"_seopress_social_twitter_img_height":0,"_seopress_redirections_value":"","_seopress_redirections_enabled":"","_seopress_redirections_enabled_regex":"","_seopress_redirections_logged_status":"","_seopress_redirections_param":"","_seopress_redirections_type":0,"_seopress_analysis_target_kw":"","footnotes":""},"categories":[29],"tags":[],"class_list":["post-7946","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-vacuum-forming"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/posts\/7946","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/comments?post=7946"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/posts\/7946\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/media\/7945"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/media?parent=7946"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/categories?post=7946"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/tags?post=7946"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}