I still feel the sting of one long afternoon in the shop.
A vinyl vacuum bag gave up mid press.
Air hissed.
The caul floated.
My jaw dropped.
Glue oozed and the door panel warped.
That single mishap pushed me toward polyurethane film.
I built a fresh bag.
Heat and pressure followed.
The new sheet flexed yet held every curve.
That small upgrade changed my veneer routine for good.
This guide shares the same lesson with you.
You will find tested picks, clear specs, and plain advice.
The goal is simple.
Help you choose the best polyurethane sheets for any woodworking task.
Quick Picks for Busy Builders
These options have earned trust on real benches.
- VS Elite and VS Extreme film for custom vacuum bags and frame presses
Lubricant infused surface
Welds with vinyl cement
Width to one hundred eight inches
Holds deep negative pressure and stretches far
- PSI Urethanes precision cast sheets for industrial parts
Tight thickness tolerance
Wide hardness range from very soft Shore OO to hard Shore D
Ideal for dies gaskets and press pads
- Universal Urethane cast sheets for everyday needs
Common sizes like twelve by twenty four inches
Hardness from forty Shore A to ninety Shore A
Good value for short runs
- Plan Tech clear sheets for windows guards and jig covers
High clarity plus solid tear strength
- McMaster Carr sheet stock for fast fixes
Many sizes ready to ship
Perfect when you need material tomorrow
Choose the right thickness and hardness.
Any of these will serve if matched to the job.
What a Polyurethane Sheet Is
A polyurethane sheet is a solid plastic film or plate that bends then springs back.
It shrugs off cuts.
It grips wood without dents.
Cold weather does not make it brittle.
Wood shops use two main kinds.
- Thin thermoplastic film at twenty to thirty mil thickness for vacuum membranes and frame press skins
Needs stretch and puncture strength
- Thick cast sheet from one eighth inch upward for press pads die backs jigs bumpers and seals
Needs load support and tear strength
Remember the difference.
Brush-on polyurethane finish is a liquid top coat.
A polyurethane sheet is a tool not a coating.
Core Specs That Guide the Choice
A few key numbers steer each buy.
- Durometer hardness measured on the Shore scale
Shore A covers soft to medium elastomer
Shore D covers very hard plastic
- Thickness
Film sits near twenty to thirty mil
Cast sheet ranges up to one inch or more
- Elongation
Good film can stretch five or six times its length without tears
- Tear strength
High values resist veneer corners and stray staples
- Compression set
Low set lets the sheet rebound after squeeze
- Temperature range
Most film softens a little at one hundred fifty Fahrenheit yet stays stable for wood glues
- Chemical notes
Many films release polyvinyl acetate glue easily
Epoxy may need a light spray release
- Surface finish
Lubricated film slides over work and loads faster
- Tolerance
Precision sheets stay within tight thickness bands which helps on dies
Check the job then match the spec.
Picking the Right Durometer
Soft feels kind.
Hard feels tough.
Here is a simple map.
- Shore OO 25-70 very soft gel like inserts
Rare in wood shops
- Shore A 20-60 soft to medium
Great for vacuum membranes
Grips without bruising veneer
- Shore A 60-90 medium to hard
Fits press pads squeegees bumpers and seals
- Shore D 50-75 very hard
Serves high load wear parts
Rare in furniture work
Typical picks:
-
Vacuum bag film at soft to medium Shore A with twenty to thirty mil thickness
-
Caul pad at seventy to ninety Shore A with one quarter inch thickness
Why Polyurethane Beats Vinyl Rubber and Silicone
I began with vinyl because it was cheap.
Failures stacked up fast.
Polyurethane film lasts more cycles than vinyl.
It stretches farther and stays flexible in cold.
Rubber bags can mark faces and smell.
Silicone releases glue well yet tears at seams and lacks rebound.
Polyurethane presents the best mix of life stretch and grip.
Head to head:
- Versus vinyl
Poly costs more but saves rejects
- Versus latex rubber
Poly handles sharp corners without thinning
- Versus silicone
Poly grips cauls better and resists tear
Vacuum Pressing With Polyurethane Film
Pressing veneer is where this film shines.
Even force reaches every inch.
Clamps stay on the wall.
Tools You Need
- Vacuum pump able to pull at least twenty five inches of mercury
- Polyurethane film
Twenty mil for light work
Thirty mil for heavy use
- Stem and fittings in brass
- Cauls or platens with breather grooves
- Breather mesh for large panels
- Release media such as plastic film or paper
- Vinyl cement like HH 66 for seams
- Glue choice: polyvinyl acetate for veneer urea formaldehyde for flat layup epoxy for curved lamination
Build a Simple Flat Bag
- Cut two film sheets larger than the panel.
- Clean seam zones with acetone.
- Brush thin cement on both seam faces.
- Wait until tacky.
- Press the seam with a hard roller.
- Add the stem port with cement and clamp.
- Seal three sides and leave one open mouth.
- Test with the pump and patch leaks.
Daily Press Routine
- Sweep the inside for splinters.
- Stack veneer caul mesh and platens.
- Slide the stack in.
- Seal the mouth with a clean bar.
- Pull vacuum and watch the gauge.
- Warm the panel if glue likes heat.
- Hold until cure.
- Open the bag and lift the piece with care.
- Clean glue before it fully hardens.
Bench Tips
- Round sharp caul corners.
- Use a plywood skin to spread load.
- Place the bag on a clean board.
- Keep a patch strip ready.
- Write cure times on tape stuck near the pump.
Bonding and Seaming Polyurethane Sheets
Good seams start with clean film.
- Wipe both sides with acetone.
- Apply a thin cement coat to each.
- Wait for tack.
- Align on a straight edge.
- Roll firmly.
- Let cure untouched.
For high stress spots add a lap strip inside.
Cutting and Shaping Cast Sheets
Thick sheet cuts like dense rubber.
- Score thin stock with a sharp knife and snap.
- A band saw with fine teeth handles curved lines.
- A scroll saw suits small shapes.
- A table saw with a sharp carbide blade rips thick parts.
- Sand edges lightly to avoid heat glazing.
- Drill with standard bits and back up with scrap.
- Punch holes with a lubricated die for gaskets.
Work slow to keep heat low.
Polyurethane Versus Other Plastics
You will meet four common materials in sheet form.
| Material | Stretch | Tear strength | Memory | Common use |
| — | — | — | — | — |
| Polyurethane | High | High | High | Vacuum bags pads bumpers |
| Polyethylene | Low | Medium | Low | Cutting boards slides |
| Vinyl | Medium | Low | Low | Cheap bags covers |
| Silicone | Medium | Low | Medium | Release film high heat |
For veneer and curved lamination, polyurethane wins.
Thickness Guide
Use these ranges as a start.
- Vacuum membrane for small work: twenty mil
- Heavy membrane or sharp edges: thirty mil
- Frame press skin: thirty mil
- Curved press pad: one quarter to one half inch at seventy to ninety Shore A
- Gasket bumper: one eighth to three eighth inch at sixty to ninety Shore A
- Cutting surface: one quarter to one inch at seventy to ninety Shore A
Product Notes
VS Elite and VS Extreme Film
- Thickness: twenty and thirty mil
- Slick surface aids loading
- Bonds with vinyl cement
- Holds deep vacuum
PSI Urethanes Precision Sheets
- Thickness: as thin as five thousandths inch up to three eighth inch
- Hardness: covers Shore OO through Shore D
- Tight tolerance suits dies and jigs
Universal Urethane Cast Sheets
- Sizes: twelve by twelve and twenty four by twenty four
- Hardness: forty to ninety Shore A plus one Shore D option
- Works for pads bumpers and general shop parts
Plan Tech Clear Sheets
- Clarity close to glass
- Good tear resistance
- Perfect for jig windows
McMaster Carr Stock
- Ships fast
- Wide size list
- Handy for small orders
Cost and Value
Polyurethane film costs more than vinyl yet saves time and wood.
Think in cycles rather than price per square foot.
One ruined curved door costs more than a premium film bag.
Cast sheet cost rises with thickness and hardness.
A quarter inch twenty four inch square in eighty Shore A lasts for years.
Common Mistakes and Fixes
- Slow leak
Spray soapy water on seams and watch bubbles then patch.
- Glue sticking
Use release film or light spray.
- Wrinkle imprint
Load on a flat board and pull film smooth before vacuum.
- Grit pinholes
Keep a plywood base under the bag.
- Loading fight
Choose film with a slick surface.
- Puncture by sharp corner
Ease caul edges and guard veneer points with scrap.
Safety Storage and Care
Work in a ventilated area when using solvent cement.
Wear gloves.
Clean film with mild soap or alcohol.
Store bags flat or hung on wide hooks.
Avoid sharp folds.
Keep film out of direct sun for long days.
Label each bag by thickness with a paint marker.
Design Uses Beyond Veneer
Cast polyurethane serves many small shop tricks.
- Soft pads on parallel clamps keep cherry faces smooth
- Stops on a sled damp noise
- Self healing leather cutting board
- Anti rattle strips on carts
- Grippy feet on jigs
Once you keep scraps on hand ideas multiply.
A Note on Market Confusion
Many readers type best polyurethane sheets then land on pages for liquid top coats.
Sheets and finishes share a name yet serve different roles.
Finish adds protection to wood.
Sheets press shape or cushion work.
Keep this split clear as you search and buy.
Frequently Asked Questions
- What brand works best for vacuum pressing*
VS Elite and VS Extreme serve most custom bags.
- How does polyethylene differ from polyurethane sheets*
Polyethylene is slick and stiff while polyurethane stretches and rebounds.
- Is polyurethane the same as urethane*
Most shops use both words for the same family of plastics.
- How durable is a polyurethane sheet*
Film lasts hundreds of cycles when treated with care.
- Can I repair a polyurethane bag*
Yes use solvent cement and a patch strip.
- Will epoxy stick to polyurethane film*
Many epoxies release clean yet testing a small spot is wise.
- What thickness should a first bag use*
Twenty mil suits small panels and thirty mil suits daily heavy work.
- What hardness works for a press pad*
Choose seventy to ninety Shore A at a quarter inch or more.
Build Steps for a Custom Vacuum Bag
- Measure your largest panel and add eight inches on each side.
- Cut film sheets or one folded sheet to size.
- Clean seam areas.
- Spread thin cement on matching edges.
- Wait for tack.
- Roll the seam straight and tight.
- Bond the stem flange.
- Seal sides leaving a wide mouth.
- Install a tape bar or fold clamp.
- Pull vacuum and mark leaks for repair.
- Write size and thickness on the corner.
Bag ready.
Press away.
A Lesson I Will Never Forget
I once left a brass screw in a caul.
Vacuum dropped the film onto that hidden spike.
Pop.
The job failed.
Now I run a magnet wand and a hand sweep before every load.
That quick habit saves both sheet and nerves.
Final Checks Before You Buy
- Define the task: membrane or pad.
- Pick a thickness range.
- Pick a durometer range.
- Look for thickness tolerance.
- Choose weldable film if building bags.
- Order a sample when possible.
- Plan clean storage.
Choose once and enjoy years of smooth pressing.
Next Step
Grab the film that fits your work.
Build a bag or cut a pad.
Feel the even pressure on that first curved panel.
Snap a photo and share the grin.
Your shop just leveled up.