Urea formaldehyde foam insulation (UFFI) is a type of insulation that was popular in the 1970s and 1980s. However, it is now recognised as a problematic insulation material in wall cavities for several reasons:

1. Health concerns: UFFI can release formaldehyde gas, which can cause respiratory irritation, headaches, and other health problems. Formaldehyde is a known carcinogen.
2. Deterioration: Over time, UFFI can deteriorate and lose its insulating properties. When this happens, it can become crumbly and release formaldehyde gas into the home.
3. Moisture retention: UFFI can absorb and retain moisture, which can lead to mold growth and rotting of the surrounding wood structures. This can compromise the structural integrity of the building and lead to costly repairs.
4. Fire hazard: UFFI is flammable and can contribute to the spread of fire in the home.
5 .Environmental concerns: UFFI is not an environmentally friendly insulation material. It contains formaldehyde, which is a volatile organic compound (VOC) that contributes to air pollution and can have adverse effects on the environment.

In summary, Urea formaldehyde foam insulation (UFFI) can pose health risks, deteriorate over time, retain moisture, pose a fire hazard, and have negative environmental impacts. Due to these issues, UFFI is no longer used as an insulation material and should be removed if it is found in wall cavities.