Tefillin Straps: An Overview


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[By Rabbi Yair Hoffman – 5TJT]

In light of the recent controversy surrounding Tefillin straps, it is perhaps a good idea to provide our readers with a background on some of the halachic issues involved. It seems that a sea-change has occurred in how Tefillin straps have been produced in recent years, in that virtually all of the manufacturers apply a plastic chemical or film on top of the leather strap and then they dye the plastic coating itself. This article will give the reader some of the halachic issues involved in order to better understand the implications of what happens when things go wrong.

As a basis for this overview, this article began with a work on the laws of STAM (Sefer Torah, Tefillin and Mezuzos) written by Rav Shlomo Ganzfried zt”l, the author of the Kitzur Shulchan Aruch. The work is called the Keses HaSofer, with an associated super-commentary which he called the Lishkas HaSofer. The information contained in chapter 23 of the Keses HaSofer was supplemented in this article with additional information from other sources and Poskim. Other important works on the subject are Rav Yaakov Meir Stern’s “Mishnas HaSofer” (Bnei Brak 5752) and “Zichron Eliyahu” by Rav Dovid Aryeh Morgenstern and Rav Eliyahu Gitman (5749). This is still a work in progress, but it was felt that since the issue of Retzuos is of particular pertinence now, it would be proper to share the information below.


The leather used in the production of Tefillin straps must be from a pure animal or fowl. Examples of pure or Tahor animals are a cow, a sheep, a goat, a deer, or a chicken. It is preferable, however, if it came from a calf’s skin (See MB 32:210 citing the Eliyahu Rabbah). The reason is twofold: 1] so that we be reminded of the sin of the golden calf and that we not sin further and 2] In order to atone for that sin of our forefathers, since there is no one that is completely free of that sin (see Sanhedrin 102a). The use of calf skin is recommened in all matters of Tefillin not just the straps. It seems, however, that this Mishna Brurah is rarely observed because of practical difficulties in obtaining calfskin.


It is a Halacha handed down by Moshe at Har Sinai that the Tefillin straps must be black on the outside. One must be very careful that the straps always be black and as dark black as possible. If the blackness has faded, it is necessary to blacken the straps again. Many Poskim hold that the side section of the strap, where the cut has been made must also be black.

At times the straps may be smeared with an oil. If an impure oil called “Fishtrawn” is used it does not create a halachic problem because the smearing does not cause the black. The main coloring comes from a pure animal – the oil merely comes to brighten the color and to soften the leather (See Noda BiYehuda MT 3, 4). Nonetheless, ideally one should be careful to obtain kosher fat or oil.

The blackening must be performed by an adult Sabbath observing Jew with the proper intent. If it was blackened without the proper intention or if it was performed by a gentile, the straps are invalid – even post facto. Even if the Jew went and reblackened them it is still not effective to render them valid. If he has no other straps available he should blacken the underside and that would be effective, but ideally he should obtain another set of Tefillin straps.

If the straps were blackened by a woman there is a debate among the Poskim as to whether it is valid or not. If other straps are unavailable a blessing may be recited upon it.

If the straps were blackened by a child and an adult is standing behind him and telling him to have the proper intentions in mind then a blessing may be recited upon these straps if no other pair is available. If there is no adult standing with him then a blessing is not recited.


There is an opinion cited in the Ohr Zaruah (Siman 564) that both sides of the Tefillin Strap should ideally be blackened as this is beautifying the Tefillin. The Beis Yoseph cites this Ohr Zaruah but writes that this is not the custom. A few years ago, however, one of the Tefillin strap manufacturers began the process of double black sides.


A very pertinent question is whether the black coloring must be permeated into the leather or if the Tefillin Straps must just appear to be black. Since, in the past few decades the Tefillin strap manufacturers have added a layer of plastic to the process, and they dye the plastic itself this question is very pressing. The Maharsham in his Daas Torah cites the responsa Gur Aryeh (#8) who deals with a case where Sofrim affix glue to the Tefillin strap and afterward they blacken the glue with ink. He questions whether it is a Halacha taught by Moshe at Har Sinai that the Tefillin straps themselves must be black and whether something in between the strap and the color would make the strap unfit for use. The Gur Aryeh tries to prove from the Gemorah in Sanhedrin (48b) and from Menachos 35a that there is no problem concerning the color being on the strap itself. Both proofs that he cites can easily be refuted, however. Indeed, the Chayei Adam in his Nishmas Adam 14:3 (cited by the Mishna Brurah) writes that if it can be peeled in one swoop, it is unfit for use. Rav Backshi Doron (Responsa #3) rules that if the leather underneath the plastic is white then the Tefillin straps are completely unfit for use.


Are there requirements as to what may be used to achieve the necessary coloring? The Gemorah in Shabbos (28a) states a drashah regarding the verse discussing Tefillin (Shmos 13:9) “L’maan teheye Toras Hashem b’ficha in order that the Torah of Hashem be in your mouth” that only items thata re permitted to be eaten by your mouth may be used. Rashi in Megillah (24b) and in Gittin (45b) seems to indicate that this requirement negates the use of gold since it is not an item that is considered “permitted in your mouth.” Rashi elsewhere in Sanhedrin (48b) seems to negate the use of gold in Tefillin not because of this drashah, but rather because of a Halacha taught by Moshe at Har Sinai. Finally, Rashi in Menachos (42b) indicates that the issue with gold, at least in regard to the Tefillin boxes is that they are an interpolation – a Chatzizta blocking. Seemingly, this would only apply to the Battim and not to straps.

Many Poskim cite the first reason in Rashi as being applicable to Tefillin production. Rabbi Akiva Eiger (on Mishnayos Megillah 37) disagrees with Rashi as to whether a non-food product such as gold can be disqualified with the idea of “not being permitted in your mouth.” Some authorities explain that Rashi rules that gold is invalid because it is not subject at all to the rules of Kosher and non-Kosher because of the drashah (This is the opinion of the Divrei Chaim 2:7 among others).

The reason why all this is pertinent is that although gold is not utilized in Tefillin strap manufacturing, other non-edible items that are similar to gold in non-edibility are used. Why lime may be utilized in processing even though it is not considered “muttar beficha” is because there is none left after the processing is completed. If, in fact, it is determined that a non-edible laminate is used to color the Tefillin black, and that laminate is still in existence afterward, then the issue of non-edible items is indeed quite pertinent. The three opinions are cited in the Yad Remah in his commentary on Sanhedrin 48b.


Prior to the blackening of the leather strips, the leather must have been processed Lishma, for the sake of Tefillin use. The source of this ruling is in the Rambam. Many Poskim are of the opinion that this is, in fact, this is a Biblical requirement. The biblical requirement of Lishma is applicable to the straps. In regard to parchment, however, the requirement seems to be less stringent. Some authorities hold that it is only Rabbinic in origin.


What is the reason why the straps must be processed Lishma, with the correct intentions? The Mogain Avrohom (cited by the Biur Halacha 33:4) writes that it is because of the Biblical requirement that the straps be black. If so, the straps must be processed and blackened with the correct intention – Lishma. It would seem that the explanation of the words of the Mogain Avrohom is that since it is impossible to blacken the straps without having first processed them, then the processing itself must perforce have the same requirement as the coloring. Since the requirement for the black coloring is biblical, it follows that is also a requirement that it be done with the proper intent in mind.

The Pri Magadim, however, poses a question on the Mogain Avrohom. He asks: What difference does it make if the blackening of the Tefillin must be done Lishma? Perhaps there is no need to process it at all! The Prim Magadim cites the Levush that the reason for the Ivud is so that the leather will be softened for the wrapping and the tying of the Tefillin.

Rav Shlomo Ganzfried (Lishkas HaSofer 23:1) provides a third reason. He cites Rav’s statement in the Gemorah in Sotah (17a) that it was in the merit of our forefather Avrohom that his children merited Tefillin straps on account of his statement that he did not even take as much as a shoe-string from the spoils of war. Shoe strings are generally processed so that they are easily wrapped and tied – therefore the requirement may also exist in regard to Tefillin straps.

Finally, Rabbi Ganzfried suggests that the Rambam may have had a different version of the Talmud and that he is quoting a Braisah that is no longer extant in our hands.

Regardless, as to which of the four reasons it is generally accepted that the requirement is biblical.


If they were not processed with the proper intention, then the skins are invalid for use as Tefillin straps. Simply blackening the leather straps with the right intentions is not sufficient. The Tefillin straps may be constructed from the skin itself or even from parchment. If someone had general intent to manufacture this parchment for the holy use of either a Sefer Torah, Tefillin, or Mezuzah, it is unclear in the Poskim as to whether that parchment may be used as a Tefillin strap.


Often, animal skins are salted very soon after slaughter in order to preserve them. The salting of the skin is generally considered to be the initiation of the “Ivud” – the processing (See Shabbos 75b and Rambam Hilchos Shabbos 11:5). If the skin was salted without the proper intent or if it was done by a gentile there is a debate as to whether one can rectify it when it is further processed with lime or Afatzim with the proper intent. There are places where skins are imported from outside of Israel and the gentiles salt them there so that they will not begin to deteriorate in transit. When they arrive in Jewish hands, he immediately rinses them and begins to process them with lime and with the proper intent. While these may be used for parchment or for the making of the Battim, it is preferable not to use them for the Tefillin straps. The reason for this is that the Chazon Ish (OC 6:1) is unsure whether this would be permitted. Even though the indication of the wording of the Mishna Brurah is that it is effective, it is preferable to be concerned for the Chazon Ish.


The width of the Tefillin strap is the subject of a three-way debate among the Rishonim. Most Rishonim rule that it must not be less than the length of a barley grain, with its peel. This is the view of the BaHag (28), the Rif, the Ittur, the Eshkol, the Rosh, and the Rambam. The source for this is from the Midrash Tanchuma in Parshas Bo (#14).

Other Rishonim (Orchos Chaim, Kol Bo, and SMaK) write that the width of the Tefillin strap should be the length of a barley corn but that it is valid even if it is equivalent to the length of a wheat kernel.

A third opinion (the SMaG and the Tur) is that even if it is is slightly less than a barleycorn or a wheat kernel it is still valid. The Bais Yoseph, however cites the Rishonim who disagree with the SMaG. Rav Karo rules in his Shulchan Aruch (OC 27:11) that if it is less than a barleycorn it is invalid.

So what is the size of a barleycorn? The Rambam writes that this is approximately half of the width of an average adult male thumb. Since many authorities write that the halachic measure of a thumb is 2.5 centimeters, this would yield a figure of 12.5 millimeters. Rav Moshe Feinstein (IM YD III #67), however, writes that the Rambam’s approximations are not applicable in our times.

The Mishna Brurah writes that the length of a barleycorn is equivalent to three times the width of a barleycorn. The Chazon Ish measured barleycorn widths to be 3.57 millimeters and concluded (Kuntrus HaShiurim #7) that it must be at least 10.71 millimeters, but not to be lenient with less than eleven millimeters. Rav Chaim Noeh (Shiurei Torah p.274 #37) writes that the width is ten millimeters, but if very necessary one can rely on nine millimeters.


The length of the Tefillin straps of the Shel Rosh on both the left side and the right side should reach to the belly-button or slightly above it. There is an opinion (that of the Shimusha Rabba) that the right strap should reach the Bris Milah. As far as the Shel Yad, ideally, it should be long enough to wrap seven times around the forearm and the three wrappings on the hand itself. B’dieved it can be just long enough to wrap around three times. If either was made longer it is still perfectly acceptable.


1) The first step is after the slaughtering of the animal the skin is salted in order to preserve it for processing. There may be a significant delay between the processing of the skin and the slaughter, so the salting is necessary to avoid decay.

2) Next, when the skins arrive in the Tefillin strap factory they are soaked in water. The salt is thus removed and the skins are softened. The section of the skin that impedes the tanning process is melted away in the water and thus separated. Dithiocarbamate (a biocide) is added to the water to prevent bacterial growth that can ruin the leather.

3) Lime (Calcium Hydroxide) or Milk of Lime and sodium sulfide (or a different disulfide reducing agent) are then added to the water in order to burn off the hairs and another fatty layer of the underside of the skin that impedes the tanning process. Lime, of course, is a base that burns similar to an acid, but is on the opposite end of the ph scale. The lime and chemicals also open up the pores of the leather that will allow other tanning chemicals to be added later to enter into the leather.

4) The remaining flesh and hairs are then removed from the skin.

5) The leather is then further soaked in water and acids are added. The acids counteract the chemical effects of the lime (which is a base.) The acid will bring down the ph of the collagen in the leather to prepare it for the chrome that is to be added. The lower ph is necessary for the chromium complexes to be able to fit into the skin between the fibers and the residues of the collagen. The acid also preserves the skin so that it will not further decompose or deteriorate.

6) The chrome (or Chromium Sulfate) is then added to the bath. This effects the essential tanning process. Chromium Sulfate increases the protein chains in the skin by some 70 percent which allows the Tefillin straps to be easily moved. The skin at this time appears to be blue in color and that is why in some of our Tefillin straps there appears to be a blue inside color.

7) This is known as “wet blue.” In order for the Chromium Sulfate to enter the skin, it must be physically rolled into it.

8) The ph is then raised by adding Sodium-bicarbonate, a base that negates the acid. The temperature is also raised to 104 degrees Fahrenheit (40 degrees Celsius).

9) Some add gallnut at this point.

These are the basic steps of the processing of the leather. The cutting and the coloring involve additional steps. It is important to note, however, that each of the above steps must be done Lishma. Merely turning on a faucet to allow the water in the mixture would not be sufficient according to many Poskim. The water must be placed in the mixture with Koach Gavrah – human power. The water must therefore be hand drawn, according to most Poskim.

Ideally, all section of the process should be done by hand in order to fulfill the requirement of Lishma. Poskim, however, have ruled that one cannot disqualify the machine processing.

As far as the coloring process is concerned, more information will hopefully be forthcoming upon our meetings in Israel.

The author can be reached at [email protected]

(Source: 5TJT)


  1. Thank you Rabbi Hoffman for sharing this important information.
    I have forwarded it to my sons in Israel.
    An old friend from Patchogue (Steve)

    }There is an opinion cited in the Ohr Zaruah (Siman 564) that both sides of the Tefillin Strap should ideally be blackened as this is beautifying the Tefillin. The Beis Yoseph cites this Ohr Zaruah but writes that this is not the custom. A few years ago, however, one of the Tefillin strap manufacturers began the process of double black sides.{

    One needs to remember, that before he wants to be machmur and use Ratzuiyas/straps with black on both sides. He should ask a Rav if he is permitted to do so. As you understand, that since this is Torah M’Sinai you need to know what is mekubal as your minhag or the accepted halacha.
    I know their are Rabbonin, and Rebbe’s that do not agree to change the custom. Since It was not done in their previous generations. Come to thing of it. 50 or even 100 years ago it wasnt so hard to paint it black on the other side. and they didn’t do it.
    I’m not saying that if your father and Grandfather had tifilin like that you shouldn’t.

  3. With regards to all black retzuos, there are 3 possible reasons why one would make or use them.
    1) In order that the back side be black, as mentioned in the comment above and as is the opinion of the Rambam. However, we are not noheg like this and until recently some makers produced a small amount of retzuos that were painted black on the backside or some individuals would choose to blacken the back side.
    2) In order for the sides to be black as per the opinion of the keses hasofer. While most were not noheg like this, a major posek in STaM told me around 10 years ago that this was a hiddur. Again, some makers used to produce a small amount of these retzuos and some individuals used to paint the sides of their own retzuos to fulfill this opinion.
    3) Having nothing to do with having the back or the sides black, the primary reason for the recent production of the all black retzuos is not due to chumra but because the entire retzuah is black through and through and hence when any of the upper layer of paint wears or cracks, the surface below it remains black. This prevents the retzuos from ever becoming bedieved or passul due to lack of paint. The fact is that the majority of people with the regular retzuos are wearing bedieved or passul retzuos due to missing paint. Those who are medakdek bemitzvos are not free of this problem as the common problematic spots where the paint wears are often not easily noticeable and goes unnoticed. Furthermore, many of us are good intentioned and want to check our retzuos or see a need to touch them up but as we are in a rush to and from davening we often forget or push it off for later and only remember the next morning and this goes on and on. For those who know how to check retzuos and so so and who know that they will touch them up that day can continue wearing regular retzuos. However, for the rest of us, to risk and likely miss out on mitzvas tefillin due to the fact that some don’t recommend the all black retzuos due to an issue of mesorah is a very serious question. I see it as an es laasos. Perhaps if our level of yiras shamayim was at the point where we’d be certain to not put on our tefillin without checking and touch them up as needed we’d not need to make such retzuos the norm however, facts have proven that they serve a very important need.

  4. One of the retzuos makers, who produces retzuos under both machshirim, told me that salting is one of the differences between these 2 machsirim of the avodas yad retzuos. One permits a gentile to salt the hides while the other doesn’t. There is discussion if the rinsing of the hides after salting voids the tanning process that started with the salting. I’m not sure if this is the basis of the machshir who is lenient or if he holds that the salting is not the initial stage of tanning. Rabbi Hoffman, can you look into this?

  5. Kudos to Rabbi Hoffman on a thorough and educational article.

    For clarification, a small retzuos maker was the first to come out with the black through and through straps. The double sided black retzuos (but natural leather color in between) had been made for years on a very small scale by most of the avodas yad makers for a select clientele. This small maker of the black through and through retzuos had some initial trouble getting the leather to die a proper shade of black. (I had shown a sample of the retzuah below the regular painted surface to Rav Friedlander, Rav Elayshiv, Rav Shternbuch and Rav Shlomo Zlaman Ulman (Kiryat Sefer) [in that order] and got 3 opinions (not black, bedieved black and black) so I gave up on them. However, within a few years, all the makers started producing the black through and through.

    As the point of these retzuos is that the surface below the regular paint is black and will prevent one from wearing passul or bedieved retzuos due to missing paint make sure that the all black retzuos are in facr died a kosher shade of black. it is now rare but if you are concerned then ask. if the died part is not lack then they are the same as wearing the original type of retzuos.

  6. update to #4.
    This maker no longer makes under 2 hechsherim. There is still inventory available but when that runs out in a year or so there will be no more makers selling 2 retzuos with a choice of hechsher.

  7. Upon rereading this article I want to make a few more comments.

    1) It is incorrect to say that many poskim require that the sides of the retzuos be black. This is the opinion of the Keses Hasofer and is not halachah lemaaseh. Most disagree.

    2) The blackening agent used can be either from a kosher animal species (burnt bone) or synthetic.

    3) No mention has been made of machine made retzuos in which the painting is done electronically with a machine sprayer.

    4) While it is true that almost all the makers put a layer of synthetic glue type material on the surface of the leather before painting , once dry, the leather is sanded to completely remove anything on the surface. I am going to investigate further but it is my understanding that the paint still soaks into the leather.

    5) One of the machshirim of mehudar, avodas yad retzuos doesn’t require that the salting be done lishma. The Edah Charedis requires it be done lishma however, I was just told by one of the makers than Rav Bronsdorfer zt”l held it wasn’t necessary. There is also difference of opinion among machshirim as to what has to be done manually.