Can I use a polyester finishing putty or a filler on a urethane front bumper?

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If it's sagging, then find some way to brace it, but if it's a case where the material has a pit or something then you should use a some polyurethane rod like this and "weld" the area in. You can sand it down and have the right finish you want. You can also use 2-part epoxies or a Bondo type filler on areas that are rigid, but remember that they will break out if flexed too much.

https://www.urethanesupply.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=URE&Product_Code=5003R1

copied from MSTANG

Automotive Aftermarket
Truck Line EZ Sand Flexible Parts Repair
08276, 400 mL, 6 per case

Two-part epoxy used to repair most plastic parts, including bumper covers, and other plastic body panels (not for use on SMC/fiberglass). Use 3M™ Polyolefin Primer 05907 for system II plastics. 10 minute work time, 30 minute sand time, 4 hour cure time

Buyer's Part Number : 08276
GTIN(UPC/EAN) : 0 00 51135 08276 8
3M Id : 60-9800-3708-3

ADDITIONAL INFORMATION
Automatic mixing. Designed to be used as a filler and adhesive. Epoxy based for easy sanding. Formulated for excellent feather edge.Flexible through a wide range of temperatures.

CHARACTERISTICS
Clamp Time
1 Hour
Color
Gray
Cure or Dry Time
4 Hour
Work Time
10 Minute
3M 1995-2001


I had asked that question earlier and didnt get the answer I was looking for.
But I found it today at a Auto Body Shop supply store.

Its called REMOV ALL Stripper, it comes in a spray can and it states that it works on all of the normal metal surfaces and also works on TPO Bumpers, Rubber Seals. I have not used it yet but I thought I would find my old Thread and add this info to it. In looking for my thread I found yours.

I have used a soft epoxy (2-part) on the bumper before.

I can't remember the name of the stuff, but it worked great.

It's been in the front bumper for several years, no issues.


I'll see if I can find the stuff next time I'm in the parts store...


jason