Tree sap leaves behind a sticky residue that later hardens. Oil-based products such as petroleum jelly loosen and break down the sap, but they leave behind a dark stain on fabrics such as nylon that is even more difficult to remove. Harsh chemical solvents break down nylon fibers and therefore also aren't suitable for sap removal. If you have a nylon jacket marred by sap, you instead must remove as much sap as possible manually, then carefully apply a mild solvent so you don't cause further staining or damage to the jacket.
Removal of fresh, sticky sap is difficult because the sap tends to spread around and work deeper into the nylon fibers. It can take days for the sap to harden completely, but you can speed up the process by freezing the jacket. Place the jacket in a plastic bag prior to freezing. It takes at least two hours for the sap to freeze completely. After it hardens, scrape as much sap from the jacket as possible with a butter knife or spoon. Refreeze the jacket if the sap begins to soften during the removal process.
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Traditional oil-based removers aren't recommended for nylon due to the increased chances for staining. Plain rubbing alcohol acts as a solvent that breaks down the remaining sap residue but is mild enough that it doesn't damage or melt the nylon fibers. Blot the alcohol directly onto the sap stain using a clean cloth. Rub gently to loosen the sap but avoid spreading it to unaffected areas of the jacket. Rinse out the alcohol promptly so it doesn't damage the nylon fibers.
Sap that has soaked deeply into the nylon may still feel hard or leave a light stain, even after the alcohol application. Use additional alcohol and a soft-bristled toothbrush to further loosen and work the sap out of the fibers. Work from the outer edges of the sap stain toward the center so you don't spread the stain over a larger area. Rinse the jacket frequently between scrubbing and alcohol applications so you rinse out the loosened sap instead of spreading it around.
Rubbing alcohol can eventually weaken the nylon fibers or lighten the color of the jacket, so prompt washing is necessary to ensure that all the alcohol and remaining sap is removed. Refer to the care label for washing instructions, although most nylon garments tolerate a regular warm-water wash cycle. Inspect the jacket for any remaining stains before drying it, as the heat from the dryer permanently sets stains. If staining does remain, repeat the alcohol treatment and wash the jacket a second time.