Multilayer tubes

A multilayer tube which comprises two or more layers containing Layer (a) and Layer (b), wherein

• at least one pair of Layer (a) and Layer (b) are disposed adjacent to each other,
• the Layer (a) contains an aliphatic polyamide composition (A),
• the Layer (b) contains a semi-aromatic polyamide composition (B),
• the aliphatic polyamide composition (A) contains a polyamide (A1), a polyamide (A2) and an elastomer polymer (A3),
• the polyamide (A1) is an aliphatic polyamide having a melting point measured in accordance with ISO 11357-3 of 210° C. or lower, and having a ratio of methylene groups to amide groups of 8.0 or more, and contained in the aliphatic polyamide composition (A) in an amount of 40% by mass or more and 85% by mass or less,
• the polyamide (A2) is a polyamide other than the polyamide (A1) and contained in the aliphatic polyamide composition (A) in an amount of 10% by mass or more and 30% by mass or less,
• the elastomer polymer (A3) contains a constitutional unit derived from an unsaturated compound having a carboxyl group and/or an acid anhydride group, and contained in the aliphatic polyamide composition (A) in an amount of 5% by mass or more and 30% by mass or less,
• an absolute value of a difference in solubility parameter SP values of the polyamide (A1) and the polyamide (A2) [|(SP value of polyamide (A1))−(SP value of polyamide (A2))|] is 1.8 (MPa)1/2 or more and 5.5 (MPa)1/2 or less,
• the semi-aromatic polyamide composition (B) contains a semi-aromatic polyamide (B1) and/or a semi-aromatic polyamide (B2),
• the semi-aromatic polyamide (B1) and/or the semi-aromatic polyamide (B2) is/are contained in an amount(s) of 60% by mass or more,
• the semi-aromatic polyamide (B1) contains 60% by mass or more and 100% by mass or less of a semi-aromatic polyamide (B11) and 0% by mass or more and 40% by mass or less of a semi-aromatic polyamide (B12),
• the semi-aromatic polyamide (B11) contains 50 mol % or more of an aliphatic diamine unit having 4 or more and 8 or less carbon atoms based on whole diamine units of the semi-aromatic polyamide (B11), and contains 50 mol % or more of a dicarboxylic acid unit which contains at least one kind selected from the group consisting of a terephthalic acid unit, an isophthalic acid unit and a naphthalene dicarboxylic acid unit based on whole dicarboxylic acid units of the semi-aromatic polyamide (B11),
• the semi-aromatic polyamide (B12) contains 50 mol % or more of an aliphatic diamine unit having 9 or more and 12 or less carbon atoms based on whole diamine units of the semi-aromatic polyamide (B12), and contains 50 mol % or more of a dicarboxylic acid unit which contains at least one kind selected from the group consisting of a terephthalic acid unit, an isophthalic acid unit and a naphthalene dicarboxylic acid unit based on whole dicarboxylic acid units of the semi-aromatic polyamide (B12),
• the semi-aromatic polyamide (B2) contains 60% by mass or more and 100% by mass or less of a semi-aromatic polyamide (B21) and 0% by mass or more and 40% by mass or less of a semi-aromatic polyamide (B22),
• the semi-aromatic polyamide (B21) contains 50 mol % or more of a xylylene diamine unit and/or a bis(aminomethyl)naphthalene unit based on whole diamine units of the semi-aromatic polyamide (B21), and contains 50 mol % or more of an aliphatic dicarboxylic acid unit having 4 or more and 8 or less carbon atoms based on whole dicarboxylic acid units of the semi-aromatic polyamide (B21), and
• the semi-aromatic polyamide (B22) contains 50 mol % or more of a xylylene diamine unit and/or a bis(aminomethyl)naphthalene unit based on whole diamine units of the semi-aromatic polyamide (B22), and contains 50 mol % or more of an aliphatic dicarboxylic acid unit having 9 or more and 12 or less carbon atoms based on whole dicarboxylic acid units of the semi-aromatic polyamide (B22).