Name: lim

Message: Could you guide me as to what to use to dye soft white polyurethane (sponge like) material into a solid color? I saw the disperse dye but there is no polyurethane, tried dylon multi purpose and the color is light and not solid flat. Thank you in advance.

Polyurethane might be better dyed in the manufacturing process, adding the dye to the liquid before it is turned into a foam. If that is not possible, then there are several possible alternatives, but I have not tried any of them on polyurethane foam myself, and can share with you only what I have read. Most questions I'm asked about polyurethane concern stretch fibers, such as Lycra Spandex, which are made from polyurethane. (See How to Dye Spandex.)

Disperse dye, which is used on most synthetic fibers and is the only option for dyeing polyester, can be used to dye polyurethane, but the washfastness is poor, and the heat required may damage the polyurethane. It can be used for pale shades, but I don't recommend that you acquire disperse dye just for this purpose. (See Dyeing Polyester with Disperse Dye.)

The acid dye that makes up a part of Dylon Multi Purpose dye is almost certainly a leveling acid dye, as is found in most all-purpose dyes. What temperature did you apply it at? Perhaps a warmer temperature for a longer period of time, and/or a larger concentration of dye in your dyebath, and/or adjusting the pH with an acid, would help. I would recommend that you try heating it in the dye gradually for an hour or more at 40°C or above (104°F), possibly with the addition of some vinegar (try 100 ml of distilled white vinegar, 5% strength, for every four liters of dyebath). Leveling acid dyes can be used on polyurethane, using a dyebath at temperatures between 40°C and 60°C (104°F and 140°F). The washfastness of leveling acid dyes is not very good, but they tend to produce solid colors more readily, at least on wool; performance on polyurethane might be different. See my page on Leveling Acid Dyes (Kiton type Dyes).

Dylon Multi Purpose dye ought to work, but don't try other sorts of Dylon dye. Dylon Permanent dye, Dylon Hand dye, Dylon Machine dye, and Dylon Cold Water dye are all fiber reactive dyes which work only on natural fibers. Under some circumstances, reactive dyes can be used as acid dyes, but there's no reason to try that unless you are already a user of reactive dyes.

Metal complex dyes (premetallised or premetalized) are more washfast on polyurethane than other acid dyes, but I've read that it is necessary to avoid 1:1 acid dyes because the lower pH required may damage the polyurethane.  1:2 metal complex dyes are good for polyurethane, though the dyes are likely to be less level (less likely to produce a single solid shade). In the US we can buy a 1:2 metal complex dye as ProChem's Washfast Dye in jet black, and in several of the dyes in the Lanaset dye range. (See "About Lanaset Dyes", and "Which Lanaset dye colors are pure, rather than mixtures?". KraftKolour in Australia also sells metal complex dyes for use in hand dyeing; ask them, before buying, which are 1:1 and which 1:2 metal complex dyes. (There are many factories in Asia making these dyes, but most do not sell in quantities small enough to be sutitable for hand dyers.)

Industrially, chrome dyes may be used on polyurethane, with better washfastness, more evenly solid colors, and lower material costs. However, I strongly recommend against the use of chrome dyes, which are used with a separate solution of hexavalent chromium, potassium dichromate, a known human carcinogen and dangerous industrial pollutant. I do not know of a source for chrome dyes for the hand dyers, though dangerous potassium dichromate is often used as a mordant with natural dyes.

If you succeed in dyeing your polyurethane foam, but in spite of your best efforts find that it is not sufficiently washfast afterwards, you should be able to fix the dye with a cationic dye fixative, such as Retayne, or Batik Oetoro's DyeFix. See Commercial Dye Fixatives.

Much of my information on dyeing polyurethane originally came from the book "Blends Dyeing", by John Shore, published by the Society of Dyers and Chemists in the UK.

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