Is it essential for the ihram garments to be new?

With regard to the izaar (lower garment or waist wrapper)
and rida’ (upper garment) for the man in ihram, the Sunnah is that they
should be white and clean; it is not essential that they be new. 

Ibn Qudaamah said in al-Mughni (10/76): 

He should wear two clean garments, namely the izaar and
rida’, because the Messenger of Allah (blessings and peace of Allah be upon
him) said: “Let one of you enter ihram in an izaar and rida’ and sandals.” 

It is mustahabb for them to be clean, either new or washed,
because we like for him to be clean in his body and also in his clothing. It
is better for them to be white, because the Prophet (blessings and peace of
Allah be upon him) said: “The best of your garments are those which are
white; dress your living ones in them and shroud your dead ones in them.”
End quote. 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 

It is not essential for the izaar and rida’ to be new, but it
is mustahabb to enter ihram in two clean white garments; the cleaner the
better, because Allah is Beautiful and loves beauty. End quote. 

Majmoo’ al-Fataawa by Ibn ‘Uthaymeen,
22/12