Francis Brown et al. define תַּ֫חַשׁ as a kind of leather or skin of animals such as dolphins and sheep.
Francis Brown, Samuel Rolles Driver, and Charles Augustus Briggs, Enhanced Brown-Driver-Briggs Hebrew and English Lexicon (Oxford: Clarendon Press, 1977), 1065 (Logos ed.)
†I. תַּ֫חַשׁ S8476, 8477 TWOT2503 GK9391, 9392 n.m. taḫaš, a kind of leather or skin, and perhaps the animal yielding it (prob. the dugong, cf. Arabic تُخَسٌ (tuḫasun) dolphin, Thes 1500 Di-Ry Ex 25:5 Post BADGER; Assyrian taḫšu (Dl Baer Ezech. xvi), for which Dl. 77 ff.; 705 conj. meaning sheep(skin); Bondi Egyptiaca 1 ff. cp. Egypt. ṯḥś, leather; v. summary of views M’Lean-Shipley BADGERS’ SKINS);—abs. ת׳ Nu 4:6 +, תָּחַשׁ v 8 +; pl. תְּחָשִׁים Ex 25:5 +;—leather used for (woman’s) sandals Ez 16:10; elsewhere for cover of tabernacle Nu 4:25, עוֹר ת׳ v 6, 8, 10, 11, 12, 14, עֹרֹת (הַ)תְּחָשִׁים Ex 25:5; 26:14; 35:7, 23; 36:19; 39:34 (all P).