Masah alal khuffayn means to wipe over khuffayn instead of washing your feet during wudu.

After thoroughly studying the inherent qualities of leather socks, our illustrious Fuqaha suggest that non-leather socks should resemble leather socks in the following:

1.   They should entirely cover both the ankles.
2.   Both socks should independently be free from holes to the extent of three small toes.
3.   They should be durable enough that a person can walk with the sock for three miles without them tearing.
4.   The socks should remain on the leg without it being tied or fastened.
5.   They should be such that water does not seep through them when water is poured over them.

[Al Mabsoot lil Sarakhsi (1/18, 184 Dar al Fikr), Al Muheet al Burhani (1/343, Al Majlis al Ilmi), Ahkam al Quran lil Jassaas (3/440, Dar al Kutub al Ilmiyyah), Tuhfa al Mulook (1/33, Dar al Bashaair al Islamiyyah), Majma al Anhur (1/75, Dar al kutub al Ilmiyyah), Al Bahr ar raaiq (1/191, 192 Dar al Ma’rifah), Tabyeen al haqaaiq (1/52 Dar al kutub al Ilmiyyah), Al Fatawa al Hindiyyah (1/32, Dar al fikr), Ad Dur al Mukhtaar (1/269, Dar al fikr), Tuhfa al Ahwadhi (1/278, Dar al kutub al Ilmiyyah), Al Maslak adh Dhaki (1/29, Wajidi Publishers), Fatawa Mahmoodiyyah (5/195, Farooqiyyah), Fatawa Haqqaniyyah (2/216, Dar al Uloom Haqqaniyyah), Kifayah al Mufti (2/321), Farouqiyyah, Fatawa Darul Uloom Zakariyyah (1/509-5516, Zam Zam Publishers)]

Yes, the socks can be used for masah while travelling. The period for which masah can be made is extended to 72 hours for a traveler (musaafir.)

For a MUQEEM (one who is not considered a traveler) masah alal khuffayn is valid for a period of 24 hours.

For a MUSAAFIR (traveler) the period permissible for masaha alal khuffayn is 72 hours.
The period of 24 or 72 hours will be reckoned from the time the wudhu (after which the khuffayn were put on) breaks, not from the time the khuffayn were put on.

For example, a muqeem makes wudu at 6 p.m. and after completing his wudu he puts on khuffayn. At 8 p.m. his wudu breaks. Twenty-four hours will be reckoned from 8 p. m. Hence, it will be permissible for him to make masah alal khuffayn each time he makes wudu until 8 p.m. the next day.

Upon expiry of 24 hours masah alal khuffayn will no longer be valid. When the period of (24 hours for the muqeem and 72 hours for the musaafir) expires, the KHUFFAYN should be removed and the FEET washed. It is not necessary to renew the WUDU.

Draw the fingers of the right hand on the upper surface of the khuffayn starting from the toes and ending (the masah) at the foreleg (just above the ankle). The masah should be done once only on each sock. The right hand should be used for the right khuff and the left hand for the left khuff.
If the back of the hand was used to make the masah, it will be valid. However, one should not unnecessarily depart from the correct Sunnah method.

It is not permissible to make masah on the side or at the under surface of the khuffayn. It is FARDH to make masah on each sock to the extent of three full fingers i.e. the full surface area of three fingers must be drawn from the toes to the foreleg.

The following acts will nullify the masah which was made on the khuffayn:

1. All things which nullify wudu.
2. Removal of the khuff (sock).
3. The expiry of the period i.e. 24 hours for the muqeem and 72 hours for the musaafir.

If only one sock was removed then too, it is waajib to remove the other one and wash both feet even if only the foreleg is exposed by lowering the khuff, it will be regarded as if the whole sock has been removed. It will then be COMPULSORY to remove the khuffayn and wash both feet.

1. It is not permissible to make masah on a khuff which is torn to such an extent that an area equal to the size of three small toes is exposed. It is permissible to make masah on the sock if it is torn less than this.
2. If the seam of the khuff comes loose, but while walking the foot is not exposed, masah on such khuffayn will be valid.
3. If a muqeem who has made masah alal khuffayn goes on a journey before the expiry of 24 hours, then his masah may be extended to 72 hours. His masah will now be valid for 72 hours.
4. If a musaafir who has made masah alal khuffayn returns to his home town then his masah will be valid for only 24 hours.
5. If ghusl becomes compulsory then masah alal khuffayn will not be permissible even if the valid period has not yet expired. The khuffayn must be removed when the ghusl is taken and the feet washed.
6. If after making masah one sets foot in a puddle of water and water enters the khuff wetting more than half the foot, then masah will be nullified. Both khuffayn must be removed and the feet washed.